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Book I 


(Other than Waterproof Glues) 



Formerly in charge, Section of Wood Preservation, Forest Products 
Laboratory, Madison, Wisconsin 

With an Appendix 

Methods of Testing Animal Glues at the Forest Products Labo- 
ratory, Madison, Wis., in which is set forth the standards 
of the Bureau of Aircraft Production, U. S. Army 

Published By 



Copyrighted by 

The Periodical Publishing Co. 

Grand Rapids, Michigan 




When the United States entered the great war 
and it became necessary to build airplanes by thou- 
sands, very definite specifications and satisfactory 
methods of testing glues were sorely needed. The 
problem of developing specifications and methods of 
test was turned over to the Forest Products Labora- 
tory and was worked out under my direction. 

This book is based largely on the results that 
were obtained, and which were applied in practically 
all purchases of glue during the war by both the 
Army and Navy Departments. General information 
on the manufacture and use of glues is given, and a 
description of the methods of testing that are described 
in the literature on the subject. 

Acknowledgement is made to Mr. A. T. Deinzer of 
Monroe, Mich., who contributed valuable information 
used in compiling this book; also to Mr. Geo. M. 
Hunt of the Forest Products Laboratory for valuable 
suggestions and criticisms and for contributions to 
parts of the text, and to Mr. L. J. Markwardt, Mr. A. 
C. Knauss, and Mr. Wilbur Lloyd Jones, of the Forest 
Products Laboratory, for contributions to the text. 



CHAPTER I General Discussion 

(Earliest Record of Glues) Distinction between Glues 
and Gelatine General Process of Animal Glue Manu- 
facture Resulting Variation in Properties Deter- 
mination The Peter Cooper Grades 11 

CHAPTER II Miscellaneous Glues 

Fish Glues Liquid Glues Vegetable Glues Casein 
Glues Blood Albumin Glue Silicate of Soda 15 

CHAPTER III Uses of Glue- 
Paper Paper Boxes Books Straw Hats Wall Paper 
Matches Leather Goods and Belting Textiles 
Writing Tablets Woodworking 19 

CHAPTER IV Glue Testing (Preliminary) 

Preliminary Examination Absorption of Moisture 
from the Air Appearance Selecting of Samples 
Surface and Other Bubbles Odor Gloss Color 
Fracture Foam "Keeping" Qualities 23 

CHAPTER VGlue Testing 

Evidence of a Single Test not Conclusive Moisture 
Ash Acidity Grease Water Absorption Melting 
Point 27 

CHAPTER VI Viscosity 

Types of Viscosimeters Engler Viscosimeter the U. 
S. Government Standard Viscosity Determination at 
U. S. Forest Products Laboratory Value of Viscosity 
Test .. 31 

CHAPTER VII Jelly Strength 

The Finger Test Lipowitz Test Edmund S. Smith 
Testing Apparatus Jerome Alexander Value of 
Jelly Strength Test 37 


CHAPTER VIII Strength of the Glued Joint 

Joint Tests Indicate Quality of Workmanship Rather 
than Glue Strength Selection of Woods for Glue Tests 
Variation in Application of Glue and Manufacture of 
Joint Application of the Load The Spandau Test- 
British Royal Aircraft Test Aeronautical Inspection 
Directorate (England) Method Shear Test and Ten- 
sion Test A Widely Used Method Discarded at Madi- 
son, Wis. The Forest Products Laboratory Shear Test 
A Modification of Madison Standard Test Miscel- 
laneous Tests Plaster Rod Test Setterburg Test 
Gill Test 41 

CHAPTER IX Plywood Strength Test 

Equipment and Method Adopted as Standard at the 
Forest Products Laboratory, Madison, Wis 57 

CHAPTER X Specifications 

Bureau of Aircraft Production, U. S. Army Specifica- 
tion for Handling and Testing Hide Glue U. S. Gov- 
ernment Standard Specification for Hide Glue Certified 
in Airplane Construction 63 

CHAPTER XI Results of Tests on Miscellaneous 
Glues.... 71 

CHAPTER XII Grading the Glue Sample 

Jerome Alexander and Peter Cooper Grades Compared 
Table of Viscosities and Jelly Strengths for Alex- 
ander Standard Grades 77 

CHAPTER XIII Some Interesting Strength 
Data on Glues 

Woods that give Strong Joints Scratched Joints 
versus Smooth Joints Laminated Construction Re- 
sistance of Animal Glues to Moist Air 81 

CHAPTER XIV Use and Application of the 
Glue Hydrometer 85 


Methods of Testing Animal Glue at the Forest Prod- 
ucts Laboratory, Madison, Wis., 1919 Standards of the 
Bureau of Aircraft Production, U. S. Army 87 


IT is said that glue has been known and used for 
thirty-three hundred years. Furniture found EARLIEST 
in tombs of the ancient Egyptians of the period RECORD OP 
of the Exodus was dovetailed, and joined with glue and GLUES. 
nails. Romans, of the time of Cicero, were familiar 
with glue, and it was in extensive use in England 
during the reign of Queen Elizabeth. 

The term glue is used in its broadest sense to de- 
note an adhesive. Used in this sense it includes a great 
variety of substances. The oldest and best known of 
these is animal glue. Animal glue comes in an almost 
infinite variety, due to the differences in methods of 
manufacture and the source and quality of the 
materials used. Glues or adhesives are also produced 
from starches, casein, blood albumin and sodium 

In general, animal glue is a substance akin to gela- 
tine, though not identical with it, and is produced from 
the bones, sinews, hides, etc., of animals. It is difficult DISTINCTION 
to define the difference between glue and gelatine be- BETWEEN 
cause these substances may be very similar in their GLUES AND 
composition, appearance and properties. Gelatine, GELATINE. 
however, is usually used for purposes in which absence 
of taste, odor and color, together with a firmness of 
jelly are desired. It is often used in foods. Con- 
sequently it is prepared from selected materials free 
from decomposition. Glue, on the other hand, is 
usually used for its adhesiveness, and lower grade 
materials and less care may be employed in its pro- 

It is rather important for a glue user to have a 
clear idea of the difference between glue and gelatine 
and of the method of manufacture of glue. A true 
conception of this may cause him to change his 
methods of glue handling. The frequently heard state- 
ment that gelatine is a pure form of glue is not strictly 
correct. Neither glue nor gelatine occurs as such in 





nature. They are formed by heating certain animal 
tissues in the presence of water. The action is 
chemical, not simply one of solution. A portion of the 
water molecule, according to recent ideas, combines 
chemically with the animal matter, the technical term 
describing the action being "hydrolysis." This action 
proceeds rapidly at a high temperature, and slows 
down as the temperature is lowered. Hence both time 
and temperature are important factors in glue making. 
As the action proceeds, a series of products is formed, 
each one differing slightly from the one from which it 
was produced. While neither glues nor gelatines are 
produced in this way commercially, we may consider, 
for our purpose, that the first one formed is gelatine. 
Continued action produces first very strong viscous 
glue, then weaker and weaker glues, until finally, if 
the action is continued long enough, a product is 
obtained that will not form a jelly when cold, and 
which has no adhesive properties. It makes no 
difference whether the heating occurs in the glue 
maker's boiler or in the wood user's shop room. When- 
ever the glue is heated in the presence of water, 
chemical action occurs which steadily reduces the 
quality of the product.* 

The process of making animal glue is, briefly, as 
follows: The stock is washed and treated to remove 
dirt and grease, then boiled to convert the glue-form- 
ing substances into a glue solution, which is concen- 
trated by evaporation until it will form a jelly on 
cooling. The jelly is then dried and the resulting 
product is the glue. 

There are many details and variations in the steps 
above outlined which depend upon the kind of stock 
used and the plant in which the glue is made, all of 
which have more or less effect upon the character of 
the resultant glue. For instance, bones are sometimes 
boiled without first removing either dirt or grease. 
This naturally fails to produce a high-quality glue. It 
is common practice to treat bones with acid to remove 
the calcium salts before cooking, but this is not always 
done. In cooking, the temperature and time have to be 

*See Rideal (Glue and Glue Testing), page 10. 


carefully watched, as over-cooking may materially re- 
duce the strength of the glue. The stock is usually 
boiled several times, using fresh water each time. .The 
first boiling or first run gives the best glue, the 
strength of the glue obtained from the succeeding 
boilings being less each time. Sometimes two or more 
boilings from the same kettle, or boilings from dif- 
ferent kettles, are mixed together or "blended" before 
the liquor is concentrated. 

The solution of glue from the boiling kettles is too 
weak to form a jelly which can be handled, so it must 
be concentrated. This is done by boiling off the water 
in vacuum pans until the percentage of glue in the 
solution is high enough to make a firm jelly on cooling. 
If the temperature gets too high during the con- 
centrating process the quality of the glue may be 

When sufficiently concentrated the glue solution is METHODS OF 
cooled by refrigeration, either after being run into COOLING. 
pans or as it runs upon a traveling belt. As it cools 
it forms a jelly firm enough to handle. The jelly in the 
pans is removed, sliced with wires or a knife, and 
placed upon screens to dry. If a belt is used the jelly 
is formed in a continuous sheet, which is cut into sec- 
tions and placed on screens as it travels along. The 
screens are then placed in a drying chamber and left 
until the glue is dry. The glue may be easily injured 
during the drying process if the temperature condi- MISCELLANEOUS 
tions are not properly controlled. The form of the FORMS. OF 
glue when dry depends upon the shape in which it was GLUE - 
placed upon the screens. If carefully sliced to the 
proper thickness regular shaped cakes will be formed. 
The sheet glue from the belt breaks into thin irregular 
shaped pieces as it comes from the drying nets. This 
is commonly run through a machine to break it into 
smaller pieces, in which shape it is shipped as flake 
glue. Other miscellaneous forms of glue are also 
made, and any of them may be subsequently ground 
and sold as ground glue. 

Sometimes mineral matter such as barium sulphate, 
white lead, chalk, or whiting is added to the glue 
after it has been concentrated, but before it is cooled. 


This gives it a light color and makes it opaque, which 
is a feature desired by some consumers. 

From the above very brief description of various 
steps in the manufacturing process it can readily be 
seen that the variety in character, color, fornj, 
strength, etc., of glues can be almost without limit. 
PETER COOPER A system of classification, based chiefly on the jelly 
GRADES. strength, was devised a long time ago by Peter Cooper, 

by which it is possible to group the great variety of 
glues into a relatively few classes or grades. The 
grades established by Cooper, beginning with the 
strongest, were designated, respectively, A Extra, 1 
Extra, 1, IX, 1*4, 1%, li/ 2 , 1%, % 17/ 8 , 2. There 
are now glues stronger than A Extra, and glues 
weaker than 2, for which there is no standard Peter 
Cooper grade. This system of grading, however, ap- 
pears to be but little used today by manufacturers, 
except sometimes for comparative purposes. Each 
manufacturer has his own system of grading which 
he keeps more or less secret, and to the general buying 
public the grades mean little or nothing. It is some- 
times claimed also that the Peter Cooper grades of 
today are not the same as those established long ago. 


FISH glue is made from the skins, bones, bladders, 
etc., of fish. The finest grades are made from 
the swimming bladders, and come on the market FISH 
in the product known as isinglass. It is said that fish GLUES. 
glues can be made that are practically equal in ad- 
hesiveness to hide or bone glues. 

Liquid glues are marketed in liquid form ready 
for use. Most glues are so prepared that they can be 
used cold. They are quite popular and have a large 
sale. Usually they are higher in price than ordinary LIQUI1 
animal glues. They may be prepared by special treat- G1 
ment of hide or bone glue, but very often they are 
made from fish glues. 

In recent years vegetable glues have been used in 
increasing quantities, especially for gluing veneers. 
At the start of the war the price of animal glue soared, 
and forced a very wide use of vegetable glues, STARCH 
especially in the veneer trade, where the use of animal GLUES. 
glues was practically eliminated. The commercial im- 
portance of vegetable glue is now obvious to practically 
every large user of glue. 

Most vegetable glues are made from starch and 
alkali. Some consumers seem, however, to be suc- 
cessfully gluing with starch boiled in water, without 
the addition of alkali. The most commonly used veget- 
able glues are produced from cassava flour and caustic 
soda (sodium hydroxide). During the war the short- 
age of shipping facilities prevented the importation 
of cassava flour, and much potato starch was used, 
usually where possible in mixtures of as much of the 
cassava flour as possible. Corn starch has been used. POTATO STARCH 
Other materials than caustic soda, such as tri-sodium G 
phosphate, sodium carbonate, etc., have been used. 
Sometimes the starch is treated with sulphuric acid 
(hydrolized or processed) before mixing with the 
alkali. The best qualities of vegetable glues, when 
properly made, show strength properties which com- 



pare favorably with the medium to good grades of 
animal glues. They also have certain advantages of 
use, especially that of applying cold, that are well 
known to most of our readers. Vegetable glues are 
often criticised because of their rather common prop- 
erty of staining wood. Recent work indicates that this 
difficulty is being overcome. 

The Perkins Glue Company, well known manufac- 
turers of vegetable glue, made the following state- 

PERKINS "Vegetable glue is manufactured by taking a car- 

GLUE. bohydrate such as cassava flour, the water absorptive 

property of which has been decreased or is already 
sufficiently low, but not too low, and mixing therewith 
the necessary small amount of water and dissolving 
the starch in the water by stirring in a solvent such 
as caustic soda, whereby a viscous, colloidal semi-fluid 
glue is formed having substantially the properties of 
animal glue for veneering. Some heat may be used in 
making the solution, in which case the amount of alkali 
used may be decreased." 

Ordinary glues were not equal to the demands of 
war time airplanes, and as a result the development 
of waterproof glues, especially for veneer parts of air- 
planes, received a tremendous impetus during the war. 
WATERPROOF The successful airplane waterproof glues were all made 
CASEINS AND either from casein or blood albumin. The wide use of 
BLOOD ALBUMIN these glues in the industries will without doubt result 
GLUES. after the war in their widespread adoption for in- 

dustrial purposes. Not only may they replace bone or 
vegetable glues for some purposes, but they make pos- 
sible the use of veneered and built-up wood products in 
exposed locations, formerly not possible because of the 
lack of a suitable glue. 

Casein glues in general are made from ground 
casein, calcium hydrate (slaked lime), and some form 
of caustic soda. Sometimes sodium silicate or sodium 
phosphate are used. Blood albumin glues are made 
usually from black soluble blood albumin, calcium 
hydrate, with a small quantity of sodium silicate, 
sodium hydrate, or ammonia. Often casein is mixed 
with the blood albumin. Casein glues set hard when 


cold, and are consequently termed cold glues. They 
may be used in cold press equipment. Blood albumin 
glues depend upon the application of heat to coagulate 
the albumin, and hence require heated presses for their 

Silicate of soda is successfully used as an adhesive 
in the paper box industry. There is a widespread WATER 
feeling that it may some day be used to advantage in GLASS. 
certain lines of wood work. Without doubt the very 
low cost of silicate of soda makes it an attractive 
material with which to experiment, and the results 
thus far obtained are promising. 

The Bureau of Plant Industry, United States 
Department of Agriculture, has patented an adhesive CORN OOB 
produced by boiling corn cobs in water under pressure. ADHESIVE. 
The resultant solution is concentrated and used as an 
adhesive. The product is not as yet developed to a 
commercial success, but gives great promise of suc- 
ceeding as a substitute for sodium silicate in the paper 
box industry. It is said that it will be lower in cost 
than sodium silicate. 



GLUE is used in. a great variety of industries, 
aside from its use in joining wood. Among 
these may be mentioned paper sizing, where its 
purpose is to make the surface of paper less porous, 
or to give it "glaze." Animal glue, gelatine and casein 
are used, dependent to some extent on the relative 
market costs and availability at the moment, and upon 
the quality of the product being made. 

Glue for sizing paper is usually bone glue, of high PAPER 
grade, free from foam, light in color, and containing SIZE. 
no more than the normal amount of grease. It should 
show no perceptible odor after heating a solution in 
water at 100 F. for 100 hours. Alum is sometimes 
added to this glue by the paper manufacturer to make 
a free flowing solution. 

Paper box makers prefer a quick setting hide glue PAPER BOX 
for "setting up." For "covering" a slow setting bone ADHESIVE. 
glue is used. Mixtures of animal glues with vegetable 
glues are often used, one advantage being lower cost. 

Here a product is required that is strong, flexible BOOK 
and free from color and odor. BINDING. 

Straw hat manufacturers desire a hide glue free 
from lime, color and odor. 

In wall paper, freedom from grease and objection- 
able odor is desired. 

In match making, uniformity is desirable. The 
glue is used in combination with phosphorous to assist 
in preventing atmospheric oxidation of the phos- MISCELLANEOUS 

For leather goods and belting, flexibility, tenacity 
and resistance to moisture are the desirable qualities 
in glue for leather and belting. High grade hide glues 
with linseed oil and glycerine added in small amounts 
are often used. Glycerine is said to increase flexibility, 
and linseed oil, resistance to moisture. 





USED IN Glue is used in dressing and finishing colored yarns 

TEXTILES. and threads, sizing of worsted and woolen wraps, and 

in the printing of fabrics. High grade hide glues free 
from odor and color are required. 

Tons of glue are used for writing tablets. Almost 
any grade, except the very poorest, will answer. 

A glue is valued primarily for its power of resist- 
ing rupture. This includes absence of brittleness, and 
it should have the power of yielding or stretching 
slightly before it ruptures. Glues may be found which 
are very strong if the strain is applied steadily, but 
which break under the impact of a suddenly applied 
load. A weaker b,ut more elastic sample is superior 
to such a glue for joining wood. In general however, a 
glue may be valued on a basis of its strength proper- 

Intimately related to the strength property is the 
covering capacity of glue. Its value is largely con- 
trolled by these two factors. High strength usually is 
accompanied by great covering capacity, and hence 
higher priced glues may actually cost less to use than 
lower priced ones, which require more glue to ac- 
complish the same purpose. Covering capacity is re- 
lated to three factors the water absorption, the jelly 
strength, and the viscosity of a solution of known 
strength. These tests made with accuracy will usually 
give a close indication of the grade or the value of a 

Color is important in some lines of wood work, 
being especially undesirable in high grade furniture. 
As a rule, however, a dark color should not be con- 
sidered detrimental, as absence of color may represent 
high cost or the use of undesirable and weakening 
chemical bleaching agents. 

KEEPING Keeping qualities are of some importance. Alkaline 

QUALITY OF glues are more liable to spoil or decompose, due to 
GLUES. bacterial action, than acid glues. Hence a test for 

acidity and alkalinity give an indication of keeping 
properties. Glues made from partly decomposed stock 
do not keep well, and have a bad odor when the glue 
solution is heated. Hence odor has a bearing on keep- 
ing qualities. 


A recent development is the use of glue as a filler 
in automobile tires. The lower grades of bone glue 
that formerly went largely to the veneer trade, are 
preferred. This new use of glue is of tremendous im- AUTOMOBILE 
portance to the animal glue industry, especially in view TIRES - 
of the inroads made on their market by vegetable glues. 
At the present time, only a few tire concerns are using 
glue, but the demand from this source promises to 
expand to very large proportions. 



A UNIFORM and generally adopted method of 
testing glue has never been developed, due 
largely to the variable and uncertain chemical 
composition of glue. It is exceedingly desirable for GLUE TESTING 
glue users to test their glues rather than trust wholly REQUIRES A 
to the promises of the salesman. The technique of SKILLED 
glue testing requires a trained observer and good OPERATOR. 
equipment to accomplish very much, though there are 
a few simple tests and observations that can be made 
by any one and which will give some idea of quality. 

Chemical analysis of glue does not enable one to 
select glues according to quality, and has never been 
successfully applied. Glue testing consists largely of 
physical tests, such as viscosity, jelly strength, 
strength of the glued joint, ash, moisture, odor, etc. 

War made necessary the development of methods of 
testing and specifying glue, and centered the attention 
of experts in this kind of work on the glue testing 
problem, not only in the United States, But in the 
European countries. The glue testing methods selected 
by the warring countries were naturally the best avail- 
able, and hence are worthy of the most serious con- 
sideration of any reader interested in this subject. 
One of the most successful attempts thus far made to GLUE TESTING 
develop a uniform practice of glue testing was ac- SCIENCE 
complished in the United States, where all glues for ADVANCED BY 
airplanes for both the army and navy was given a THE WAR - 
most thorough inspection. This work was done at the 
Forest Products Laboratory at Madison, Wis. Inten- 
sive investigation by a large force over several months 
on methods of testing was carried out under the guid- 
ance of a glue chemist of national reputation. All of 
the testing methods that might seem to have any merit 
whatsoever were tried. The resultant methods TESTS BY AN 
selected in this way were incorporated in a tentative AUTHORITY. 
specification which was submitted to a conference of 
glue manufacturers, and as finally evolved, had the 







approval of all. They may therefore be considered as 
the best that this country has developed thus far. 

In the following pages a few simple tests will be 
outlined that are possible to make without great ex- 
perience or complete equipment. The more refined 
tests, however, require a trained analyst, familiar with 
the manipulation of testing apparatus, and a well 
equipped laboratory. The methods of test recom- 
mended by the Forest Products Laboratory are men- 
tioned in outline only in the text, but are grouped 
together and given in full in the appendix. 

Glue should not become damp or sticky (hygro- 
scopic) in the air, or it may mold. A hygroscopic glue 
indicates adulteration with sugar, molasses, etc. The 
appearance, hardness and manner of breaking are 
points which may be used to judge quality after some 
experience. Some glues may have a cloudy or milky 
appearance, due to the presence of calcium phosphate. 
Glues of excellent strength may be warped or twisted, 
and very dark in color. Ground glue should not lump 
together in warm, humid weather. 

Samples should be taken from several parts of the 
package, as glues are very often blended from more 
than one run and the mixing may not have been 
thorough. Special attention should be given ground 
glue, which is very easy to adulterate. White bubbles 
on the surface of the glue are an indication of decom- 
position. With such samples be sure to test the odor, 
as described later. Decomposed or sour glues are to 
be avoided. Bubbles appearing deep in the glue are 
not necessarily an indication of putrefaction. An 
expert glue buyer is able to judge somewhat by ex- 
amining a flake of glue by looking through it at a 
strong light. 

Gloss on the surface does not necessarily indicate 
high quality. On the contrary, low grade glues may 
be highly glossed, while good quality glues may be 
dark, though the surface should be smooth. A uni- 
form color and surface appearance is desirable. 

Color is not a reliable indication of quality. The 
first runs of glue from the glue stock are lighter in 
color than the last ones. But it is easy to clarify glues 


chemically, greatly weakening them in the process. 
Bone glues are usually darker than hide glues, unless 
they have been bleached. With any particular lot, non- 
uniformity of color indicates either adulteration or 
blending. The addition of zinc oxide gives a white 
opaque glue, and one that sets quickly. It is also said 
to add somewhat to its water resistance. In moderate 
quantities zinc oxide is not injurious. Sometimes inert 
matter of no value is added as an adulterant. Hence 
the color of such samples may well be reason for 

Breaking a sample of the glue with the thumb and SIMPLE TEST 
forefinger of each hand gives an indication of glue FOR QUALITY. 
quality. The condition of the air must be considered, 
as a dry day will give a different indication than a 
humid one. If the glue fractures evenly and bends 
but little, low strength and brittleness are indicated. 
If a thin sheet bends well and in case it breaks, shows 
a splintery fracture, good strength is indicated. Bone 
glues show a glossy fracture ; hide glues of high grade 
never do. 

Foam in a glue is undesirable. A solution of glue 
in water may be stirred vigorously, with a rod, or 
better, with an egg beater, and a fair indication of its 
foaming properties will be obtained. Particular atten- 
tion should be paid to the rate at which the foam sub- 
sides. If it persists for long, the glue should be 

Odor is a sign of poor keeping quality. Usually ODOR SHOULD 
offensive odor is the result of using spoiled or de- BE SWEET. 
composed stock, or else it may mean that the glue itself 
has started to decay. 

Something may be learned by smelling of a 
moistened flake of glue warmed in the hand. A more 
reliable method is to heat a solution of glue in water, 
about 1 part glue to 12 of water, at a temperature of 
100 for 48 hours. It should remain sweet during this 
period. A similar sample should be able to stand at 
room temperature for four or five days without de- 
veloping a bad odor, or showing the presence of mold 
or decomposition. 



WHILE the tests just described are useful guides 
in purchasing glue in the absence of better 
methods, they are, at best, a makeshift. 
Wherever possible advantage should be taken of more TESTg ARE 
refined methods. MISLEADING. 

The reader should, however, have a rather clear 
idea of the limitations of glue testing. It is usually 
not possible to obtain a very clear idea of glue value 
from any single test that may be applied. In an article 
describing the testing and grading of glues, the follow- 
ing statement is made by E. G. Clayton (Jour. Soc. 
Chem. Ind., 1902, 21, 670) : 

"In conclusion, the observations seem to show that 
while it would be rash to form a judgment on glue 
from a single test, the evidence afforded by a number 
may be irresistible. The expert's surest system ap- 
pears to be not to rely on single short cut tests of 
general quality, but to employ a number of methods, 
including any having especial bearing on the pros- 
pective or present uses of the glue, and then to base 
his conclusions on a consideration of all the results 

Ordinary glue of good quality contains from 8 to 
16 per cent, of water. Too much water indicates poor MOISTURE 
keeping quality, and of course means that the buyer D 
is paying for that much water. Too little water may 
indicate an over-dried glue, which is injurious to its 
strength properties. Moisture as low as 5 per cent, 
is not uncommon, but a good glue should have not 
less than 8 per cent. 

Moisture is determined by heating a ground sample 
at a temperature of 110 C. to a constant weight. The 
sample being hygroscopic, must be cooled in a 

After making the moisture determination, the DETERMINATION 
same sample may be used for determining ash. It 

*See Appendix for Forest Products Laboratory methods. 






should be incinerated carefully in platinum, or pre- 
ferably in vitreosil, care being taken to prevent free 
ignition. The ash usually varies from 11/2 to 3 per 
cent. A fused ash indicates a bone glue, one not fused 
a hide glue. A large ash indicates adulteration, and 
a chemical examination will show what it is. Calcium 
phosphate is found in the ash of bone glues. 

By its reaction to litmus a glue shows whether it 
is acid, alkaline or neutral. The test is made by dip- 
ping strips of red and blue litmus paper in a glue 
solution, and noting the color change. (The solution 
left after the viscosity test may be used.) An acid 
glue turns blue litmus red, and a neutral glue will not 
change the color of either red or blue litmus. Alkaline 
glues will turn red litmus blue. A slightly acid glue 
is preferable to a neutral or alkaline glue, because it 
is not quite so favorable a medium for the growth of 
the organisms which cause the decay of glue. Strong 
alkalinity usually means an over-limed glue, which will 
almost surely cause trouble. 

To determine insoluble matter dissolve 30 grams 
of glue in one liter of hot water, and allow to stand 
for 12 hours in a warm place. Filter the hot solution 
through a weighed filter paper or good, crucible, wash 
well with hot water, dry and weigh. In hide glues 
the insoluble matter is rarely over 2 per cent. In bone 
glues it may be more. 

A little aniline color is added to the solution of glue 
in water (some of the solution remaining from the 
viscosity test may be used). The mixture is painted 
on unsized white paper and the appearance noted. 
Grease is visible in round, characteristic spots, and the 
relative amount present is indicated by comparison 
with other glues or the experience of the operator.* 

The water absorption test was proposed by Schat- 
termann in 1845. Glue does not dissolve in cold water, 
but has the property of absorbing several times its 
weight of water. Some glues will absorb eight to ten 
times their weight of water and still retain a rather 
firm consistency. Good glues will absorb at least six 

*See Jour. Soc. Chem. Ind., Feb. 28, 1906. 


times their weight. A method used by the United 
States Bureau of Chemistry is as follows: Place 10 
grams of the sample broken in small pieces in a beaker 
and cover with 200 c. c. of water at 15 C. Cover the 

11 11 e j? n *. i -.LI SIGNIFICANCE 

beaker and place in a refrigerator for 24 hours, with OF THE TEST 

the temperature between 14 C. and 18 C. Then pour 

off the water and weigh the glue. This determination 

cannot often be made above 20 C. The firmer the 

jell the greater the glue strength (in general), and the 

more water that is absorbed the greater the covering 

capacity of the glue. If the glue becomes slimy, or if 

the solution shows evidence of putrefaction, poor 

quality is indicated. 

The melting point of the glue solution is of interest 
as it is a measure of how quickly or slowly the glue 
will set. It is sometimes used as a substitute for the MELTING 
viscosity test. The test is sometimes made as follows : POINT - 
Weigh 15 grams of the sample and soak 12 hours in 
a flask with 30 c. c. of water. Then immerse the flask 
in boiling water and shake well until the glue dissolves. 
While still liquid pour some of the solution into a test 
tube and close the end with a cork, and cool for one 
hour in water at 15 C. Now place in a water bath in 
an inclined position, with a thermometer, and gradu- 
ally raise the temperature. When the glue leaves its 
vertical position the temperature may be taken as the 
melting point. 

A simpler and more accurate method is in use at 
the Forest Products Laboratory. A drop of the liquid NEW 
glue solution is run into a glass U tube of small size. MELTIXG 
The tube is then cooled in water for 10 minutes at 15 PO INT TEST. 
C. It is then placed in a water bath and the tempera- 
ture raised gradually. The melting point is taken as 
the temperature at which the slug of glue moves down- 
ward in the U tube. 

For information in the literature on the melting 
point determination see R. Kissling (Chem. Zeitung, 
1901, 25, 264 and Jour. Soc. Chem. Ind., 1901, 21, 509), 
also N. Chercheffsky (Chem. Zeitung, 1901, 25, 413, 
and Jour. Soc. Chem. Ind., 1901, 25, 731). 


THIS test is one of the most important of the 
tests made on glue, and is in universal use by 
glue manufacturers. (See Fels, Chemical 
Zeitung, 1898, 9, also Jour. Soc. Chem. Ind., 1890, p. 

Viscosity is a term used to describe the degree of TYPES O F 
fluidity of the glue solution. The thicker the solution VISCOSIMETERS. 
the higher its viscosity and the lower its fluidity or 
flowing power. Instruments for measuring viscosity 
(viscosimeters) are of various kinds. Those usually 
used for glue testing are of the orifice type, and depend 
in principle upon the time required for the passage of 
a known quantity of liquid through a standardized 
orifice, at a known temperature. 

Any viscosimeter of the orifice type may be used. 
Fels used a modified Engler (Jour. Soc. Chem. Ind., 
1890, p. 654), with a 15 per cent, solution (15 grams 
of glue in 100 c. c. of solution). Rideal preferred a 
type described by Slotte and modified as described in 
the Journal Society Chemical Industry, 1891, page 615. 
A later modification is described by Scarpa (Gazetta 
Chemica Italiana, 1910). Some observers express vis- 
cosity in the number of seconds required for the glue 
solution to pass through the orifice of the apparatus. 

- 5 * dps 

S.S g go -> .-^-2^. 

r2 Description of v, 3 o < 9 * 2 > *J 

S 6 Samples || | M g.S ||S 

1. Light yellow transparent thick ' 

plates 163 149 1.65 

2. Brown transparent glue 14.0 125 1.36 

3. Sherry yellow transparent glue 15.4 171 1.91 

4. Light yellow plates 18.2 150 1.60 

5. Muddy (truber glue) 15.2 199 2.21 




Others prefer to express it as the ratio between the 
time required for the glue solution to pass through the 
orifice compared with water at the same temperature. 
Fels, with a 15 per cent, solution at 30 C., obtained 
the results shown in the table on page 31. 

Other workers, using different instruments, ob- 
tained different figures. The value obtained depends 
upon the form of the apparatus and the size of the 

For comparative purposes only, a home made de- 
vice may be used. 

One may be made from a volumetric pipette, fitted 
with a stop cock. The lower end is heated in a glass 
flame and carefully reduced in size until its inside 
diameter is of the desired size. One recommended by 
Jerome Alexander (Jour. Soc. Chem. Ind., 1906, p. 
159) is made from a 45 c. c. pipette, and will pass 45 
c. c. of water at 80 C. in 15 seconds. It has the follow- 
ing dimensions: 

Capacity, 45 c. c. of water at 80 degrees C. 

Internal diam. of effluent tube 6 mm. 

External diam. of effluent tube 9 mm. 

Length over all of effluent tube 7 cm. 

Smallest diam. of outlet (about) 1.5mm. 

Outside diam. of bulb 3 cm. 

Length of bulb 9.5 c. 

Length of upper tube 22 cm. 

This pipette is surrounded with a water bath, and 
the flow of solution is controlled with a pinch cock and 
rubber tube fitted over the top. 

Some glue factories, where a great many samples 
have to be tested every day, use a more rapid home 
made apparatus, with an orifice so large that the glue 
solution will pass through in 10 or 15 seconds. One 
can be made from a pipette as described, or from a 
glass tube contracted at one end. For several reasons 
such instruments are seldom very accurate. 

Better control of temperature and greater accuracy 
can be had with the Engler viscosimeter. This is 
more complicated and more expensive than the pipette 
or glass tube type, and is also slower to operate, but it 





Index No.. 



Grease is not of necessity a 
serious defect in Glue, except in 
certain specific uses. It does reduce 
foam and affects adhesiveness. 


The white spots show the grease. 
O is Free of Grease. 

5 and under is Commercially Free 

6 to 20 " Normal 

21 to 35 " Slight Excess 

36 to 50 " Excess 

51 and over " Very Greasy 

Examining Chemist 

The amount of grease in the glue is indicated by the light spots. 
This sample is "Normal." 





Index No. 



Grease is not of necessity a 
serious defect in Glue, except in 
certain specific uses. It does reduce 
foam and affects adhesiveness. 


The white spots show the grease. 
is Free of Grease. 

5 and under is Commercially Free 

6 to 20 " Normal 

21 to 35 " Slight Excess 

36 to 50 Excess 

51 and over " Very Greasy 

Examining Chemist 

The large number of white spots shown in this sample indicate 
"Very Greasy" glue. 


has the advantage, in addition to greater accuracy, of 
being an instrument which is in general use for testing 
many kinds of materials. The values obtained by its EXGLER 
use are readily understood by laboratory men and can VISCOSIMETER 
be readily checked. It can be purchased from supply is 
houses standardized and ready for use. The Engler RECOMMENDED. 
viscosimeter is in use at the Forest Products Labora- 
tory, and is required by the specifications for glue of 
the army and navy. It is recommended for standard- 
ized work on glues. 

The viscosity determination is made at the Forest 
Products Laboratory as follows : One part of glue by 
weight is dissolved in 5 parts of distilled water by 
weight. The sample is strained to remove insoluble 
matter, and the viscosity determined in an Engler 
viscosimeter within five minutes after the sample has 
been melted. The viscosity is expressed in terms of 
the number of seconds required for 200 c. c. of glue 
solution at a temperature of 60 C., to pass through the 
standard orifice of the viscosimeter, compared with 
distilled water at the same temperature. 

The precaution of straining the glue before testing 
should not be overlooked. Insoluble matter may clog 
the orifice and materially affect the result. 

The viscosity test is of great value in grading glues, SIGNIFICANCE 
and is one of the most important tests that is used. OF VISCOSITY 
In general, viscosity is a gauge of glue strength, high TEST. 
viscosity corresponding to high strength. It would 
lead to great error, however, if complete reliance were 
placed on the results of this test. It should only be 
considered in conjunction with other tests. Glues pro- 
duced from the same stock, under identical conditions, 
may be graded on the viscosity test. But glues under 
test may have been produced from different stocks 
by different methods. Hence considerable error may 
be found by relying on viscosity alone. 

Acid treated bone glues give viscosities very low 
in proportion to their jelly strength. Opaque and 
colored glues give higher viscosities than clear ones of 
corresponding strength. Glue stock incompletely 
washed, or over-limed gives a high viscosity. Some 
clarified glues have a low viscosity, both bone and hide. 


Or if clarified with alum, the viscosity will be too 
high. Rabbit glues are liable to have viscosities that 
are too high to correspond with their jelly strength. 
The apparatus used may also lead to slight errors, as 
glues do not always grade the same when tested with 
different instruments. 



ONE of the most significant and important of 
the tests commonly made on glue is an esti- 
mation of jelly strength. It was suggested by 
Lipowitz in 1861 and has been extensively adopted. It 
is made on a solution of the glue in water cooled to a 
jelly in a refrigerator, and consists in an estimation 
of the strength or firmness of the jelly. In spite of 
numerous attempts to develop apparatus for obtaining 
a measure of jelly strength in terms of some tangible 
numerical unit, the finger test is still favored by those 
most expert. The finger test is akin to tea or wine 
tasting in that it requires long experience and great 
skill to obtain good results. THE FINGER 

The finger test is made on a 25-gram sample soaked TEST FOR JELLY 
in 300 c. c. of water at room temperature. Melt and STRENGTH. 
stir the solution, and place in a refrigerator for at 
least 15 hours at a temperature between 5 and 10. 
degrees C. (40 to 50 degrees F.) Test either in the 
refrigerator or immediately after removal. The 
operator uses the third finger of the left hand and 
measures the resistance by pressing on the glue jelly. 
Any difference between different samples is noted, and 
the samples may be grouped in accordance with this 

In the Lipowitz test a small pointed plunger with 
a funnel at its upper end is inserted in the jelly. The 
funnel is loaded gradually with shot until the load THE LIPOWITZ 
is just sufficient to force the plunger entirely through TEST - 
the jelly from its top surface to the bottom of the 
cylinder. The weight of shot necessary to effect this 
gives the Lipowitz number. 

An apparatus invented by Edmund S. Smith is on 
the market which makes jelly tests without breaking 
the surface of the glue. It does not give good results 
on extremely high or low grades. It is rather com- 
plicated, and requires frequent cleaning and attention. 
It consists in principle of a thistle tube, over which is 


stretched a thin sheet of rubber. At the other end of 
the tube is a bulb for obtaining air pressure, and a 
sensitive pressure gauge or water manometer. The 
pressure tube is also filled with water. The observa- 
tion is made by forcing the rubber diaphragm into 
THE SMITH the glue jelly with air pressure from the bulb. The 
JELLY TESTER, measurement of jelly strength is made by noting the 
pressure on the gauge or manometer, and the amount 
that the diaphragm is forced into the glue is measured 
or controlled by a reading of the water level in the 
pressure tube. The jelly strength is measured on the 
gauge or manometer. The apparatus must be adjusted 
uniformly on the different samples to fee tested, and 
the distortion of the diaphragm must be the same in 
each test. The apparatus is covered by patent No. 

Jerome Alexander (Jour. Soc. Chem. Ind., 1906, 25, 
p. 160) describes a device "consisting of a brass cylin- 
drical vessel supported like a gas tank by four vertical 
rods, against which it slides with almost frictionless 
roller bearings. This brass cup is allowed to rest on a 
truncated cone of jelly of definite size, composition and 
temperature. Shot is gradually poured into the cup 
until a definite expression of the jelly is observed. Be- 
neath the cup are two vertical adjustable brass up- 
rights 3.5 c. m. high, connected with an electric bell 
circuit. When the cup reaches their level the bell 
rings. The weight of the brass cup, plus the weight 
of the shot, gives a figure which expresses the jelly 

After thoroughly testing most of the above 
methods, as well as numerous other ones, an apparatus 
was adopted at the Forest Products Laboratory that 
is described in the appendix. This apparatus was 
modified from one in use in the glue laboratory of 
Armour & Co., Chicago. (See Appendix.) 

The jelly test, together with viscosity, are the most 
important of the tests made on glues, and all other 
tests must be considered in conjunction with them if 
the operator is to form a true conception of the grade 
of the glue sample. Both tests must always be made 
to obtain a fair comparison between an unknown 


sample and one of Peter Cooper's standard. To say 

that a glue tests 1 Extra means that its jelly strength 

and its viscosity must be the same as a standard sample 

of Peter Cooper's 1 Extra. Obviously, the operator GLUE STANDARD 

must secure standards of known strength before he SAMPLE s ARE 

can rate his glues, as it is practically impossible to de- XEEDED - 

fine a method of test and an apparatus with sufficient 

exactness that the glue may be rated without the use 

of standards of comparison. Therefore it is of the 

utmost importance that the operator secure or have in 

his possession standards of known value before he 

can rate and value the unknown sample. Peter Cooper 

standards may be purchased from the Peter Cooper 

Glue Company. 

In making jelly strength tests it is well to re- 
member that sulphates in the glue increase the jelly 
strength (as well as viscosity), while chlorides and 
nitrates diminish it. 



EVERY user of glue in wood work is interested 
in the strength of the glue. Hence numerous ef- 
forts have been made to devise tests that would 
measure the strength of the glue in the joint. The 
literature is full of descriptions of tests of one sort 
or another, and quite frequently statements are found JOINT 
to the effect that the results obtainable are variable or STRENGTH 
unreliable. Many thousands of tests have been made TESTS MAY BE 
at the Forest Products Laboratory, Madison, Wis., and DECEPTIVE. 
as a result of these, the author is forced to admit that 
most of them do not measure the strength of the glue, 
but rather are a measure of the quality of workman- 
ship or skill of the operator in making the joint. With 
the utmost skill and the best methods of workman- 
ship, it is possible to produce joints with grades 1*4 
or higher that will always break the wood. Possibly 
the grade of 1% may be the dividing point. Dense 
maple, chosen because of its great shear strength, was 
used in these tests. Some information on grades below 
1% may be obtained by strength tests. Usually speci- 
mens glued in the factories or by the average carpenter 
fail in the glued joint many hundreds of such have 
been sent in for testing. But the same glues can be 
made to give a joint so strong that wood failures result. 
The best joints made by carpenters and workmen have 
been produced with grades about Peter Cooper No. 1. 
Glues grading higher probably set too fast, and since 
the workman does not often produce a joint 100 per 
cent, perfect, those grading below that do not develop 
the full strength of the wood. 

The glue chemist should have a rather clear un- 
derstanding of the fundamentals of testing glue joints, 
or he may draw erroneous conclusions from his results. 
He is possibly more liable to be measuring his own 
ability to do "stunts" with the glue rather than 
measure the strength of the glue. In any case, with 
grades above 1%, watch yourself closely. The strength 




test has been very useful in obtaining data on the 
effect of various operations, such as time of pressure, 
etc., on the strength of the glue joint. It is also true 
that a good strong joint cannot be obtained with a glue 
that lacks adhesiveness. 

In order to develop as nearly as possible the full 
strength of the glue it is necessary to use wood of 
good gluing qualities and of high shearing properties. 
Not all species meet these requirements. The following 
table, based on tests on small clear specimens of 
material, gives a number of species which have an 
average unit value in shear parallel to the grain of 
over 2,400 pounds per square inch at 8 per cent, mois- 
ture, as well as a number of other common species with 
shearing strength below this value. 

In general the shearing strength of wood when the 
surface of failure is tangential is about 8 per cent, 
greater than when the surface of failure is radial. This 


Specific gravity 
oven dry based 
on volume 

When oven- 
Species green dry 
Ash, white (forest grown) .52 .60 

Beech 54 .66 

Birch, sweet 59 .70 

Cherry, black. 47 .53 

Dogwood (Flowering) 64 .80 

Gum, red 44 .53 

Hickory, big shellbark 62 

Locust, black 66 .71 

Locust, honey 60 .67 

Maple, sugar 56 .66 

Oak, Canyon live 70 .84 

Oak, Commercial red 56 .67 

Oak, Commercial white 59 .71 

Persimmon :... .64 .78 

Walnut, black 51 .56 

Yew, western 60 .67 

Shear parallel to 

grain surface of 



Ra- gen- Aver- 

dial* tialt age 

2331 2021 2176 

2256 2397 2326 

2873 2811 2842 

1780 2294 2037 


1734 1900 1817 

2510 2536 2523 

2516 3391 2954 

2391 2514 2452 

2602 3030 2816 

2370 2628 2499 

1906 2263 2084 

2136 2466 2302 

2185 " 2671 242S 

1273 1552 1412 

2326 2861 2594 

* By radial surface of failure is meant a plane of failure per- 
pendicular to the growth rings. 

tBy tangential surface of failure is meant a plane of failure 
parallel or tangent to the growth rings. 

IIFrom paper by L. J. Markwardt, Forest Products Labora- 







indicates that higher values would be secured from most 
species by makir.g the surface of failures tangential, but 
in some species the reverse appears to be true. The 
radial shearing strength would be influenced to a con- 
siderable extent by any season checks which may exist 
in the material, and consequently any material contain- 
ing checks should be eliminated. 

The probable variation of the results of a single 
test from the average of the species is less for shear 
than for some of the other important mechanical prop- 
erties. This indicates that deviations from the average 
values given in the table would be smaller for shear 
than for the other properties. In general, in species 
having a shearing strength of 2,600 pounds per square 
inch about three-fourths of the pieces, without selection, 
would be expected to give unit shear values above 2,400 
pounds. The proportion of individual pieces having a 
shear strength greater than 2,400 pounds would, of 
course, be larger for species whose average shearing 
strength is above 2,600 pounds per square inch. 

The shearing strength of wood, like the other 
mechanical properties, is closely related to the density 
or dry weight of the material. In general the lighter 
species, therefore, are inferior to the denser ones in 
shearing strength, and, likewise, within a given species 
the heavier pieces would normally exceed in strength 
those which are lacking in density. The selection of 
material on a density basis consequently presents a 
method by which the poorer specimens of most species 
may be eliminated. In species having an average shear- 
ing value of 2,800 pounds per square inch, about three- 
fourths of the individual pieces 5 per cent, below the 
corresponding average density would be expected to 
give unit shear values of 2,400 pounds or over, while 
about half the pieces at 10 per cent, below the average 
density equal or exceed the latter shearing stress. 

The moisture content of the wood when below the 
fiber saturation point* is another factor which influ- 

*The fiber saturation point is that point at which no water 
exists in the pores of the timber, but at which the cell walls are 
still saturated with moisture. The fiber saturation point varies 
with the species. The ordinary proportion of moisture, based 
on the dry weight of wood, at the fiber saturation point, is from 
20 to 30 per cent. 




ences the strength, the strength increasing with de- 
crease of moisture. In general, a moisture content EFFECT OF 
above this point does not affect the strength. The MOISTURE ON 
material for gluing should, therefore, probably be at STRENGTH. 
least as low at 13 per cent, moisture. 

While a number of species have very high shearing 
values, several other points must be taken into con- 
sideration in selecting material for glue tests, such as 
the property of taking glue, and availability. Sugar 
maple has been found to give very good results, is easy 
to procure, and when straight grained and free from 
defects is recommended as a shearing material for glue 
tests. Sweet birch would likewise be expected to prove 
satisfactory for this purpose. 

The question of the significance of joint strength 
tests made on grades better than 1% has already 
been raised. It has been found that joints made at 
just the instant the glue begins to chill are very strong. 
It is almost impossible to always have the glue film of 
the same thickness in successive test pieces, and the 
thickness of the film very markedly affects the joint. 
Above all avoid a film too thin (a starved joint). A 
starved joint can be obtained by using too much pres- 
sure. It will be obvious that before the operator can 
feel that the results of his strength tests are reliable REQUIREMENTS 
he must know all the essentials of producing a perfect FOR OBTAINING 
joint, and be perfectly certain that he has succeeded MAXIMUM 
in doing so. He is advised to do considerable experi- STRENGTH. 
menting with joints made under different conditions 
before relying upon his results. 

This more properly resolves itself into a discussion 
of methods of testing. It is of course possible to ob- 
tain some information from almost any sort of 
strength test that will rupture the glued joint. Thus 
the workman may try to split the joint with a chisel. 
If it follows the glue, either he has a poor joint or the IMPROPER 
glue is weak. Such tests are relatively of very little APPLICATION v 
value, as even low grade glues may not split along the OF THE LOAD. 
joint if a soft or weak wood is used. With very hard, 
strong woods it is possible to obtain an idea of the 
strength, but not in terms that can be readily ex- 
pressed. Such tests should be carried out on strong 





woods, as maple or birch. Even oak is hardly strong 
enough in shear to test ordinary grades of glue. 

When the attempt is made to measure the load 
necessary to rupture either the wood or the glued joint, 
the results are liable to be so variable as to mean 
nothing unless properly applied. Any test that does 
not apply the load uniformly over the test piece is 
to be regarded as of doubtful value. Such tests usually 
can be resolved into applying the load on the joint in 
shear, in tension, in cleavage or by twisting. Only the 
first two should be considered by the glue tester. In 
the latter two the load is concentrated on small areas, 
which give way and allow the load to then be con- 
centrated on adjacent areas. The piece can never 
show its maximum strength, as it can when the load 
is applied uniformly. 

This is a test proposed by Karmarsch and adopted 
by the Artillerie Werkstatte, Spandau. It has been 
much used in America. Cement testing machines are 
often used, or sometimes a system of levers is devised 
that works well. Samuel Rideal (Glue and Glue Test- 
ing) reports great difficulty in obtaining check results, 
due to non-uniformity in the wood, and in the surface 
of the wood at the glued joint ; time of heating the glue 
and temperature of gluing, thickness of glue, pressure 
used, uneven application of pressure, presence of 
lumps; variation in the moisture in the air, tempera- 
ture while setting, duration of time between gluing and 
testing ; temperature while testing ; uneven application 
of load. Truly a formidable list of causes for varia- 
tion, and obviously requiring skill and knowledge of 
the subject to secure consistent results. 

The Spandau test, as officially adopted in Germany, 
consists in gluing together two blocks of wood with a 
plain butt joint with the grain end to end. The blocks 
are 40 mm. square in cross section, and 210 mm. long. 
The glue stock is prepared by dissolving 250 grams 
of glue in 500 c. c. of water. The blocks having been 
glued together, one is fixed horizontally to a table in 
such a manner that the joint between the two blocks 
overhangs beyond the edge of the table. A scale pan 
is attached to the block at a given distance beyond the 



edge of the table and weights are added until the 
'joint fractures. 

This test cannot be recommended very highly, be- 
cause it places the top of the joint at a maximum 
strain, while the bottom is in compression. A uni- 
formly applied load is much superior. 

A test adopted by the British Royal Aircraft 
factory in their specification of Nov., 1916, uses a 
double wedge shaped block (See Fig. 2). It is made BRITISH BLOCK 
by gluing together two pieces of American walnut. AIRCRAFT TEST. 

Glue Joint 
FIG. 2 

The glue solution is prepared according to the 
glue manufacturer's instructions. The test joint has 
dimensions 3 in. by 1 in., and is required to support 
a static load of 187 pounds per square inch in direct 
tension. The test is made at 122 F. at normal 
humidity, in a fully saturated atmosphere, and sub- 
merged in water. The load must be supported for 
various lengths of time in these tests, depending upon 
the grade of glue desired. 

The Aeronautical Inspection Directorate (Eng- 
land) tests a sample of the form shown in Fig. 3. 

American walnut is used and the glued surfaces 

Gluo Joint 

FIG. 3 



slightly tooth-planed. The specimen is supported at 
the ends in a testing machine and the load applied in 
ANOTHER the center. Precautions are specified for the tempera- 

BRITISH TEST, tures, pressures used in gluing, preparation and appli- 
cation of the glue, etc., that insure reasonably uniform 
results. The fundamental objection is that the load is 
not uniformly applied to the glued joint. Fairly con- 
sistent results may be obtained, however. 

Of the numerous methods experimented with at the 
Forest Products Laboratory, Madison, Wis., the ten- 
sion test and the shear test were the only ones that 
gave reasonably accurate results. The tension test 
was discarded because it does not represent the most 
common practice of gluing wood, and is furthermore 
inconvenient and slow. It can, in one form or another, 
however, be satisfactorily used to determine glue 

Glue Joints 

FIG. 4 


A test specimen as shown in Fig. 4 has been widely 
used*, but was discarded at the laboratory. This 
specimen is made of three pieces glued in the form 
shown, with 4 square inches in each joint. The speci- 
men is placed in the testing machine and tested in com- 
pression. This test appeals to people because it does 
not require a tool or special device to test in a testing 

*See Jerome Alexander (Jour. Soc. Chem. Industry, 1906, 25, 



machine. It is not recommended, however. It is men- 
tioned here because of its rather widespread use, and 
the temptation to use it in the absence of complete 
equipment. The objection lies in the fact that when 
the load is applied, the two outer pieces spread apart 
at the bottom, giving a failure in cleavage instead of u. s. ARMY 
in shear. The test as finally adopted at the Forest AND NAVY TEST. 
Products Laboratory uses a specimen as in Fig. 5. The 

FIG. 5 

wood is prepared conveniently as in Fig. 6, which is 
self explanatory. It is necessary to use a shear tool. 
A drawing of this is shown in Fig. 7. Fig. 8 shows a 
specimen under test in the testing machine. 

A complete description of the Forest Products 
Laboratory method is given in the appendix. A modi- 
fication of this method has been used to some extent by 
sawing the specimen as shown in Fig. 9. 

This specimen is then tested in compression with- 
out the use of a shearing tool. The author cannot 
vouch for this method, as he has never used it. 

A rather common method of glue testing is to cut 
a series of boards as shown in Fig. 10. These boards A SIMPLE BUT 
are glued together as the vertical straight lines in- INACCURATE 
dicate. After the glue has set, a wedge is driven in METHOD. 
at the places indicated by the arrows. The claim is 
made that a good grade of glue should always hold 
the pieces together so firmly that the glue joint does 
not give way, but that the wood itself will split or be 



Ghed Joint 

Spec\mens l -~Firs't Step 




FIG. 6 



ruptured. This method is guesswork and yields no 
results for the reason that no matter how much the 
strength of the wood may vary, the test does not in- 
dicate this variation. Furthermore, the result cannot 
be expressed in figures. 

Another common method is to glue up two pieces 
from 10 to 12 inches in length and of suitable width 
to fit into a bench vise. After the glue has dried, the 
glued boards are placed into the vise so that the 



entire joint stands out from three to four inches. The 
workman strikes the joint with a hammer, and it is 
claimed that if the glue joint is weaker than the wood 
the joint will break; if not, the wood will split. The 
results obtained in this test are absolutely worthless. 

FIG. 8 

Figure 11 shows a simple scheme that will likely 
appeal to some. 

The heavy straight vertical line represents a wall 
or post. A represents a heavy hinge being fastened 
to the wall and beam B. C represents a block, the 
end being rounded so as to fit part way into the "V" 
cut opening of the glued test piece E. D represents 
the platform of a so-called platform scale. The beam 



is 10 feet long by 4 inches by 2 inches. The test piece 
is usually 10 inches by 3 inches by % mcn each, two 
pieces glued together and the top cut out either "V" 
or "U" shaped. C is placed in the opening ; this block, 
as the illustration will indicate, being a little larger 
than the slot into which it is fitted. The weight on the 
end of the beam required to break the pieces is read 
and recorded. 


FIG. 9 

A simply made lap joint test is worthy of men- 

Carefully selected pieces of a hard wood are used 
for this test. The moisture content is determined. THIS is A 
The pieces are jointed and sized, so that they will be FAIRLY GOOD 
exactly 8 inches long by 1 inch by 1 inch. The thick- 
ness and width should be determined with a micro- 
meter. The pieces are then lap-glued as per illustration, 


FIG. 10 



and we now have a glued surface of exactly one 
square inch. In studying Fig. 12 the reader will ob- 
serve blocks B. They are glued into the corners of the 
testing machine, one being 2 inches, the other 1 inch 
thick. Par. represents a partition or wall through 
which the plunger P passes. P is a stick of wood one 
inch square of convenient length to which T, a support 
for the weights, W, is fastened. 




FIG. 11 

The glued pieces are stored in a dry room for 
from three to four weeks. The test strips are next 
placed in the testing machine upon blocks B. Weights 
are added on T until the lap breaks, and the weights 
to accomplish this are recorded. The objection to this 
method is that the load is not applied uniformly over 
the glued joint. 

Test pieces. 

6X7X7 6X1X1 

FIG. 12 


The difficulty of obtaining satisfactory results 
from strength tests on glued wood joints has inevit- 
ably led investigators to try other schemes for test- MISCELLANEOUS 
ing strength. The .experience of the Forest Pro- STRENGTH 
ducts Laboratory has led them to feel that schemes TESTS - 
for testing the strength of the film, or of some por- 
ous material such as plaster or earth cemented to- 
gether with the glue may have merit. 

A method of glue testing suggested by Karmarsh 
and modified by Weidenbusch, 1859, consists in break- 
ing small rocks of plaster of paris cast in molds of A PLASTER 
uniform size and saturated with glue solutions of R D TEST. 
known strength and dried thoroughly. They are then 
horizontally supported at their ends and loaded in the 
center, the weight required to break the rod being the 
so-called Karmarsh, or Weidenbusch, figure for the cor- 
responding glue solution. 

Setterberg (Schwed, techmks Tideskrift, 1898, 
XXVIII, 52) soaks strips of paper in the glue solu- 
tion. The excess of glue is removed with filter paper, THESE TESTS 
the strips allowed to dry, and tested in a paper testing WARRANT 

Gill (Jour. Ind. and Eng. Chem., Feb., 1915, p. 
103) tried the tension test, gluing blocks together 
endwise. He also tried porcelain, glass, and tiling. He 
could not secure uniform results, and then dipped 
filter paper in the glue solution, dried and tested. His 
conclusions are as follows : "The method of testing glue 
by measuring the strength which it imparts to bib- 
ulous paper is dependable and gives fairly concordant 



A HIGHLY satisfactory method of testing glues in 
veneer panels or plywood was developed at the 
Forest Products Laboratory. It was adapted 
from the English A. I. D. method. An experienced TEST SUIT ABLE 
operator can make from 500 to 1,000 tests a day. A FOR VENEER 
large number of tests on each glue may thus be made, WORK. 
reducing the variables due to a small number of tests. 
The specimen for this test is prepared as shown 
in Fig. 13 and the test is made by placing the speci- 


FIG. 13 

men in the grips of a testing machine and exerting a 
pull upon it. This causes the joint to fail either in the 
glue or the wood, or both. The English requirement 
is that the glue joint in the plywood must show a 
strength of at least 150 pounds per square inch in this 
test to be acceptable. On the basis of several thousand 
tests on plywood secured from various American manu- 
facturers it appeared that a minimum average of 150 
pounds per square inch may also be safely required for 
American plywood. 

*From paper prepared by Teesdale and Colgan, Forest Prod- 
ucts Laboratory. 



Fig. 14 shows the style of grips first used, as recom- 
mended by the English reports, to do away with the 
free pivot motion allowed by these grips a special jaw 
was designed as shown in Fig. 15. These jaws were in- 

FIG. 14 

serted in the Riehle cement tester as shown in Fig. 16. 
The upper jaw is hung on a knife edge, since it is a 
part of the leverage system of the balance. The lower 
jaw is rigidly fastened except for the vertical motion in 
oeprating the machine. A guide attached to it counter- 
acts the tendency of the upper jaw to swing in the di- 
rection of opening of the upper saw cut. 

When adjusting a specimen into these jaws the only 
additional precaution necessary is to make sure that 



it is centered in order to get a straight pull. This is 
done by adjustable thumb screws which control the 
position of the grips. 

The bucket attached to the lower arm at the left 
contains small lead shot, which are released by a valve- 
like mechanism and flow into the pan on the spring 
scale placed below. The load is applied to the specimen now TEST is 
in the holder by means of the wheel at the right. As MADE. 

FIG. 15 

the load is applied, the shot are released from the buck- 
et and flow into the pan on the scale, which indicates 
the actual load applied. When the specimen breaks the 
flow of shot is automatically stopped. 

The difference between the strength values shown 
in the shear test on blocks and the English test on 
plywood is due to several reasons. In the shear blocks, 



the grain of the two pieces glued together runs in the 
same direction, while in plywood the grain of the plies- 
WHY PLYWOOD runs m opposite directions. Changes in moisture con- 
STRENOTH tent due to the drying of the glue in the joint will, 

TESTS GIVE therefore cause stresses in the joint in the plywood to 
LOW VALUES. a very much greater extent than the shear blocks, be- 
cause the shrinkage of wood is much greater across 
the grain than along the grain. Also in making joints 

FIG. 16 


in thick material greater care is possible in the prep- 
aration of the surface and the application of the glue 
than in plywood. The continued flexing of plywood in 
handling also may have some weakening effect on the 

The panels to be tested are cut into specimens 
one inch by three and one-fourth inches ; the test area 
being restricted to one square inch by notches cut DETAILED 
through one face and the core, on opposite sides of the DESORIPTION 
panel, one and one-eighth inches from each end. OF PLYWOOD 

A panel should preferably be three-ply and should TESTS. 
not have a core which exceeds one-eighth inch. Thin- 
ner cores are preferable. When thick panels are test- 
ed, it is sometimes necessary to plane them down to a 
thickness suitable for the machine before testing them. 
Panels with 1/64-in. plies are too thin to test, because 
it is practically impossible to make them into shear 
specimens without spoiling them. This test may be 
used to test the quality of glue or of workmanship in 
veneer panels. It may also be used to test the water 
resistance of glups by placing the test specimens in 
water or under humid conditions before being tested. 




readers inexperienced in glue testing may 
have gained the impression that the methods of 
-*- test are unreliable and of little value. This is 
by no means the case. It is true that testing 
methods are arbitrary, and that they cannot in 
general be expressed in terms of numerical values with 
sufficient exactness to write a specification. It was THE ARMY AND 
for this reason that in the work of the Forest Products NAVY GLUE 
Laboratory, all thought of attempting to prepare a SPECIFICATIONS. 
specification without the use of a standard sample was 
abandoned. The specification as evolved makes use of 
a standard sample which was selected as being satis- 
factory for the purpose, and of a grade not difficult 
to obtain. The specification then requires the manu- 
facturer to furnish glue at least equal to the standard 
sample in jelly strength, viscosity, grease, foam and 
odor. After two years of use, covering purchases of 
over a million pounds of glue for both the army and the 
navy, it can be said that the specification was very 
satisfactory, both to the manufacturer, the consumer 
and the specification department. Hence it can be 
recommended unqualifiedly to any purchaser of glue 
in quantities sufficient to warrant the expense of 
making tests. It would only be necessary for the buy- 
er to determine upon a standard sample of the quality 
he desires, and set aside a quantity, say 50 or 100 Ibs., 
to be used as a standard sample. The specification as 
given would apply in all respects except "adhesive- 
ness," where the required strength values would change 
with the grade of the standard sample. In these speci- 
fications the standard is about the equivalent of Peter 
Cooper's grade 1. 

1. This specification covers the requirements of 
the Bureau of Aircraft Production for all hide glue 
used in the construction of propellers and for splices 
of airplane structural members. 




TEST, U. 8. 


2. The glue must be a high grade hide glue, sweet 
and free from any deleterious substances. 

3. The glue shall be tested by comparison with 
a standard sample for jelly strength, viscosity, grease, 
foam and odor. The standard sample may be obtained 
from the Director, Forest Products Laboratory, Madi- 
son, Wis. 

4. The following tests shall be made by a Bu- 
reau of Aircraft Production representative before cer- 
tifying or accepting any hide glue for use in aircraft 

5. The test for adhesiveness shall be made on 4 
test specimens of the form and dimensions shown in 
Fig. 5, page 49. The test specimens shall be made 
of maple having a shearing strength of at least 2,400 
pounds per square inch. This will require wood hav- 
ing a dry weight of about 50 pounds or more per cubic 
foot, and a moisture content of from 8 to 12 per- 

6. The glue shall be mixed with water in four 
different proportions by weight, and test specimens 
shall be prepared using the glue at each of these four 
dilutions. Unless otherwise specified, the proportions 
used shall be as follows: 

Water 1 

Glue ... 1 





The glue shall be added to the water at room tem- 
perature, stirred thoroughly, and allowed to stand for 
at least two hours. It shall then be melted in a water 
bath, at 140 deg. Fahr. (60 deg. C.) and applied to 
the wood surfaces which are to be placed in contact. 
These surfaces shall fit perfectly together, and the 
wood shall be at room temperature. After gluing, the 
test blocks shall be held under a moderate and uniform 
pressure for 15 to 24 hours. At the end of this time 
they shall be released from pressure without subjecting 
them to shock, and allowed to stand for 6 days addi- 
tional. The test specimens shall be finished so that 
when they are ready for testing they shall have a 
glued joint two inches square, and conform to Fig. 5. 
The specimens shall be tested to destruction in a test- 


ing machine approved by the Inspection Department. 
No test specimen shall fail under a load of less than 
2,200 pounds per square inch, and the average shearing 
strength shall be at least 2,400 pounds per square inch. 
Specimens which fail under a load of less than 2,400 
pounds per square inch will, if the failure occurs en- 
tirely in the wood, be excluded in calculating the aver- 
age shearing strength and the permissible minimum. 
The glue mixed with water in at least one of the four 
proportions as above shall comply with this strength 
requirement. The dilution at which the greatest 
strength is indicated will be recommended for use. 

7. The jelly strength shall be determined upon JELLY 

a mixture containing 12 parts of water to 1 part of STRENGTH. 
glue. The glue shall be soaked, melted and poured 
immediately into a vessel of standard size and shape. 
It shall then be allowed to stand for at least 15 hours 
in a refrigerator at a temperature of from 40 to 50 
deg. Fahr. (5 to 10 deg. C.). The relative strengths 
of the standard sample and the glue under test will 
be determined in the refrigerator, or immediately after 
removal therefrom, by pressure with the fingers or 
with some suitable apparatus approved by the Inspec- 
tion Department. 

8. The viscosity shall be determined in an Eng- VISCOSITY. 
ler Viscosimeter upon a sample containing 1 weight 

of glue to 5 weights of water. The sample shall be 
strained and the viscosity shall be determined within 
5 minutes after having been melted. The viscosity 
shall be expressed in terms of the number of seconds re- 
quired for 200 cubic centimeters of the glue solution, 
at a temperature of 60 deg. C., to pass through the stan- 
dard orifice of the viscosimeter. 

9. The relative amount of grease present shall be GREASE. 
determined by mixing a dye with some of the glue 
remaining from the viscosity test, painting the mixture 

on unsized white paper, and observing the appearance. 

10. The test for foam shall be made on the sample FOAM. 
used in the viscosimeter. The sample, after heating 

to 140 deg. Fahr. (60 deg. C.), shall be beaten for one 
minute with a power egg beater, or similar instrument, 





and allowed to stand one minute or until the foam can 
be measured. 

11. The odor of the glue, when in hot solution, 
must be sweet and must remain sweet for 48 hours; 
that is, free from any suggestion of deteriorating ani- 
mal matter. 

12. The inspector shall have free access to all 
parts of the plant where this glue is being manufac- 
tured, and shall be afforded every facility to satisfy 
himself that the glue is in accordance with this speci- 

13. The tests shall be made on a sample from each 
lot of glue. The manufacturer of hide glue, when he 
has accumulated not less than 30,000 pounds which he 
considers to be in compliance with the specification, 
will make up a sample which shall be representative of 
the whole 30,000 pounds, grind it, if it is not already 
in the ground condition, and send at least a 2-pound 
sample of it to the Senior Inspector, Bureau of Air- 
craft Production, Forest Products Laboratory, Madi- 
son, Wis., or to a laboratory designated by the Inspec- 
tion Department, Bureau of Aircraft Production. It 
must be plainly marked "Preliminary Sample," and it 
must be accompanied by a written statement as to 
the amount of the glue represented by the same and in- 
structions concerning the method of using this glue 
which the manufacturer ordinarily furnishes the user. 
He shall notify the Raw Materials Department and the 
Inspection Department at Washington, D. C., when the 
sample is forwarded. 

14. This sample will be tested by Bureau of Air- 
craft Production inspectors, and the results of these 
tests will be sent to the manufacturer as soon as pos- 

15. If the preliminary sample passes all tests, 
the manufacturer may proceed to mix thoroughly all 
the glue represented by the sample. He will advise the 
inspectors at the laboratory on what date it will be 
ready for final mixing, inspection and barreling. As 
near that date as possible, an inspector will visit the 
glue factory. In his presence, the glue will be given 


such final mixing as he deems necessary. It will also 
be packed in tight drums or barrels in his presence; 
and, at the same time, he will take a sample which will 
be known as the official sample. The inspector will METHOD OF 
forward this sample to the Forest Products Labora- SEALINO - 
tory, or to a laboratory designated by the Inspection 
Department, for analysis. The results of this analysis 
will determine whether or not the hide glue can be 
certified. After the glue has been placed in barrels, 
the inspector will witness the "heading" of the filled 
barrels, and will seal both ends of every inspected bar- 
rel with serially numbered labels provided for the pur- 
pose. Each barrel shall also be marked with the name 
of the glue. 

Note The submitting of the preliminary sample 
is not required and may be omitted if so desired by 
the manufacturer. 

16. The manufacturer will then put the inspected 
barrels in a place which is dry, sheltered and suitable 
for storage. Glue which is otherwise satisfactory, 
will be rejected if proper storage facilities are not pro- 
vided for it. 

17. If the official sample proves to be in compli- 
ance with the specification, the manufacturer will be 
notified that the lot of glue covered by the official 
sample has been certified. Certified hide glue is the 
only hide glue which aircraft manufacturers will be 
permitted to use. Hide glue which does not comply 
in every respect with this specification will not be 
certified, and its use will not be permitted on govern- 
ment aircraft contracts. If an inspected glue fails 
to be certified, the manufacturer will be required to 
remove the inspection labels. 

18. The glue manufacturer must report to the Raw 
Materials Department, Bureau of Aircraft Produc- 
tion, and to the Senior Inspector, Forest Products Lab- 
oratory, Madison, Wis., every sale of certified hide 
glue. The reports must be in duplicate and they should 
include the amount of glue, the number of the label 
of every barrel shipped, the name and address of the 
consignee, and the date of shipment (or sale). 






19. No glue which has been rejected shall be of- 
fered to any department of the Bureau of Aircraft 
Production or to any aircraft contractor to the gov- 
ernment without a full statement of the cause of re- 

1. This specification is drawn to cover the re- 
quirements of the Bureau of Aircraft Production for 
the handling and testing of hide glue at airplane and 
propeller factories. 

2. All the animal glue used in the construction 
of propellers and for splices of airplane structural 
members shall be hide glue certified in accordance with 
Specification No. 14,000-B. 

3. Soaking. The glue and pure cold water must 
be weighed out separately, and according to the pro- 
portions recommended for the particular glue by the 
Senior Inspector, Bureau of Aircraft Production, 
Forest Products Laboratory: They should then be 
mixed, thoroughly stirred, and allowed to stand in 
a cold place in a covered vessel until the glue is 
thoroughly soaked and softened. The mixture must 
stand at least two hours. 

4. Melting. After the glue has been sufficiently 
soaked, the water-glue mixture shall be melted on a 
water bath or in a carefully regulated electric heater. 
The glue solution must never be permitted to rise to 
a temperature exceeding 150 deg. Fahr. About 140 
deg. Fahr. provides an excellent working tempera- 

5. Heating. Glue shall not be heated for a 
greater length of time than is absolutely necessary. 
Glue which has been heated for 8 hours or longer must 
not be used. All the glue which has been heated at any 
time on any day shall be rejected at the close of that 
day and must not be used on any succeeding day. In 
order to prevent the loss of moisture, the glue pot shall 
be kept covered when not in actual and continuous 
use. Any skin or scum which forms on the surface of 
the glue shall be removed. 

6. Application. The glue shall be applied to the 
wood in a room which is free from draughts and as 


warm and humid as healthful working conditions al- 

7. Wood. The wood shall be uniformly dry and 
at least as warm as the air in the glue room. High 
temperatures and prolonged heating of the wood should 
be avoided in order to prevent distorting the surface. 
The wood surfaces shall "fit" perfectly and they shall 
be clean. 

8. Spreading. The glue shall be applied to both APPLY GLUE 
surfaces of the joint, and shall be spread freely and as TO BOTH 
rapidly as is consistent with good workmanship. SURFACES. 

9. Pressing. The clamp pressure or other pres- 
sure shall be applied quickly in order to prevent the 
glue from jellying or setting. A sufficient number of 
clamps should be used to insure that the wood is in 
close contact at all points, and that the pressure is 
evenly distributed. 

10. Sanitation. Only enough glue shall be mixed 
at any one time for one day's work. The glue pots, 
brushes, etc., shall be cleaned out each night with boil- 
ing water and all the glue left over after the day's 
work shall be discarded. The brushes will remain 
sweet if left over night in a solution of carbolic acid. 

11. A glue test specimen shall be made of 1-inch TEST 
boards of sufficient size to furnish ten test specimens SPECIMEN. 
conforming to dimensions specified in Fig. 5, page 49. 

The boards shall be representative of the wood on 
which the glue is to be used. The specimen shall be 
made up under the average conditions prevailing in the 
glue room. The gluing shall represent actual practice 
and no special precautions other than those ordinarily 
taken shall be employed in preparing uie glue or wood. 
The gluing shall be performed by the employes of 
the airplane factory accustomed to this kind of work. TESTS MUST 
No protective coating of any kind shall be applied to BE MADE. 
the wood surfaces or to the finished specimen. The 
specimen shall be held in the clamps for 15 to 24 hours. 
After being removed from the clamps it shall stand 
for 6 additional days in a warm, dry place. The speci- 
men shall be cut into ten shear blocks which conform 
to the dimensions shown in Fig. 5, page 49. 




12. The following test shall be made to deter- 
mine the strength of the glued joint. Ten of the 
shear blocks shall be tested in a shearing machine 
immediately after sawing, and the strength of the 
glue in shear shall not be less than that of the wood. 

13. The required strength must be obtained from 
80 per cent, of the specimens tested. 

14. Test blocks may be sent to the Senior In- 
spector, Bureau of Aircraft Production, Forest Pro- 
ducts Laboratory, Madison, Wisconsin, for this test. 
When blocks are forwarded for this test, they should 
be plainly and clearly marked and should be accom- 
panied by Bureau of Aircraft Production I. R. Form 
No. 68 (Request for Glue Tests). 

15. The inspector of the Bureau of Aircraft Pro- 
duction shall have free access to all parts of the plant 
of the manufacturer where this work is being carried 
on, and shall be afforded every reasonable facility to 
satisfy himself that the work is in accordance with 
this specification. Tests shall be made under the super- 
vision of a representative of the Bureau of Aircraft 



TESTS in accordance with the methods outlined 
in the foregoing specifications on about 30 samples 
of animal glues obtained through miscellaneous 
sources were made. The results of these tests are of T 
considerable interest, both as a guide to the operator J^HREE 
and to the prospective purchaser of glues. The results L ^ BORATORIES 
are given in Tables 1 to 9. Some of these samples 
were sent by Laboratory F to two glue manufacturers, 
termed Lab. A and Lab. N, where the tests were made 
by their own methods. The comparisons obtained are 
very interesting. 

Table 1 gives a description of the samples tested. 

The results of the viscosity tests are given in Table 
2. Since a different type of viscosimeter, and probably 
a different volume of glue solution was used by each VISCOSITY 
of the three laboratories, the results cannot be directly TSSTS. 
compared. This emphasizes the need for a standard 
apparatus and method of determining viscosities. 

In Table 3 the glues are arranged in order of their 
relative jelly strength. This arrangement shows n 
general agreement between the three laboratories as JELLY 
to which are the strong glues and which the weak. 

From the results of the various comparative tests 
described above, it might be presumed that these tests 
are of little value, and might as well be discarded. This 
is not the case, however, for while it is true that the 
results from different laboratories cannot be directly 
compared, because the methods of test are different and THE RESULTS 
because of the personal equations, at any one labora- CANNOT BE 
tory the value of a glue can be pretty closely approxi- COMPARED 
mated by the use of these tests, because they are made DIRECTLY. 
in the same way each time. The results above quoted, 
however, show, very emphatically, the need for a stan- 
dard system of testing to be followed by all glue lab- 



The reaction of the various glues to litmus is shown 
in Table 4. It seems strange that there should be such 
a disagreement among the three laboratories as to 
whether the glues were acid, alkaline or neutral. In 
most cases, of course, the reaction was very slight in 
either direction, and the difference must be due either 


Kind (Information Price* 

Sample from manufac- quoted 

No. turer.) per Ib. 

1.... ....Animal. 





Blend of fish and 








F i r s t run pure 


hide glue. 


Vegetable glue. 


V e r y high-grade 



Hide glue. 


Hide glue. 


Hide glue. 




Thin cut clear 


flake glue. 


Extra clear flake 



Medium cut clear 


flake glue. 


Highest testing. 




Pure rabbit skin 



Exceptional water 


taking qualities. 









....Pure hide elue. 



Recommended by the 
manufacturer for hard- 

Recommended for soft- 

A special fish blend joint 

Prepared paste. 
Probably a casein 

From lab. stock. Prob- 
ably foreign glue. 

Contains a large amount 
of mineral matter. 

28 High-test glue. 

"June, 1917. 


to the difference in judgment of the men who made 
the tests, or to a difference in litmus paper. 

Laboratories A and N did not report upon this KEEPING 
test. From Table 5 it is apparent that practically all QUALITIES. 
the glues would have passed a test requiring that they 
stand 48 hours without showing signs of deterior- 

Table 6 shows typical results selected at random 
from glues tested by W. L. Jones, B. A. P. inspector TY PICAL 
stationed at the Forest Products Laboratory, the RESULTS 
methods being those described in the appendix. The OBTAINED BY 
table is arranged in order of increasing viscosities, USE OP ARMY 
and is given here as it may be useful to the operator METHODS. 
attempting to use the proposed methods. 





.. 173.9 

Lab. A 




Ratio to Viscosity of Water 
Lab.N Lab.F* Lab. Af Lab. NJ 

23.00 3.30 1.24 1.53 
21.00 2.69 1.19 1.40 
20.75 2.82 1.21 1.38 
20.75 2.65 1.19 1.38 
20.5 4.18 1.26 1.37 
25.00 5.48 1.40 1.67 
22.5 3.04 1.20 1.50 
24.25 4.39 1.32 1.62 
23.00 3.76 1.29 1.53 
18.25 1.62 1.05 1.22 
24.00 3.11 1.24 1.60 
25.00 4.70 1.32 1.67 
23.00 3.43 1.29 1.53 
24.00 4.03 1.31 1.60 
21.5 1.21 1.43 
27.5 4.98 1.83 
22.00 2.56 1.23 1.47 
26.25 4.14 1.34 1.75 
22.25 2.73 1.20 1.48 
20.75 2.34 1.14 1.38 
21.25 2.56 1.18 1.42 
25.00 3.62 1.27 1.67 
15.75 1.40 1.00 1.05 
23.25 1.24 1.55 
27.00 4.90 1.39 1.80 


148 4 















... 261.8 






".'. 257.7 

*Compared with the viscosity of water at 20 C., which is 
52.6 seconds in this instrument. (Engler.) 

fConipared with the viscosity of water at 60 C., which is 
about 42 seconds in this instrument. 

^Compared with the viscosity of water at 20 C., which is 
15 seconds in this instrument. 



No. Lab. A' 

1 69 

2 64 

3 61 









13 Too low 













26 Too 

27 70 

28 72 

Lab. N* 







Lab. Ff 


NOTE In Laboratory! tests, 
the glues were classified into 
groups according to their 
strength by finger test method 
as follows, group 1 being the 

Group 1 Nos. 9, 11, 28. 

Group 2 Nos. 23, 15, 19, 18, 
17, 21. 

Group 3 Nos. 15, 5, 12, 10, 1, 
27, 20. 

Group 4 Nos. 14, 2, 25, 24, 4, 

Group 5 No. 3. 

Group 6 No. 13. 

Group 7 No. 26. 


"These values represent numerical figures obtained with the 
instruments in use at these laboratories. 
tBy finger test method. 

No. Lab. F 

1 Slight acid 

2 Slight acid 

3 Very slight 

4 Slight acid 

5 Very slight 

9 Slight acid 

10 Slight acid 

11 Acid 

12 Neutral 

13 Slight acid 

14 Neutral 

15 Neutral 

16 Neutral 

17 Neutral 


19 Neutral 

20 Acid 

21 Neutral 

22 Neutral 

23 Acid 

24 Neutral 

25 Neutral 

26 Neutral 


28 Neutral 













A Lab. N 

Very slight acid 

Very slight acid 

Very slight acid 


Very slight acid 

Very slight acid 

Very slight acid 

Very slight acid 


Fairly much acid 





Very slight acid 


Fairly much acid 


Very slight acid 

Slight acid 




Slight acid 




A very interesting series of results is published 
by Linder & Frost (Proc. Am. Soc. Test. Mat., 1914, 
Part II, page 509). Data given on moisture, vis- 
cosity, cost, and breaking strength of 25 samples of 













Lab. F 













Lab. F. 







*A11 samples discarded at the end of 334 hours, 
marked with a star were not foul at this time. 


**Time required for glue to develop an offensive odor. 

Typical results obtained by methods recommended in appendix. 




*Peter Cooper Co.'s standard, 1%. **Peter Cooper Co.'s 
standard, l*/4. ***Bureau Aircraft Production standard sample. 







I 3 




4J . 

S | 


W T3 C 


C Q) 



bo ^ 

O 05 

>s U 


2 ft 



CC ^ 

~ tin ^* 


> < 

oS 1 ! 

> 0^ 


^^ 5, 




<! 43 O 










































2 -1 






23/ 4 -l 












2 -1 























AS explained before, the kinds of glue that may 
be obtained are almost infinite in variety. In- 
deed, there is an almost unlimited variation in 
the appearance of glue samples. Jerome Alexander GRADES OF GLUE 
(Jour. Soc. Chem. Ind., 1906, 25, 158) states: "In glue, SUGGESTED BY 
above all things, appearances are deceptive. Even after JEROME 
a manufacturer has finished his glue he is obliged to ALEXANDER. 
test it in order to establish the grade of his finished 
product." Alexander grades his samples by standards 
which he keeps in his laboratory. He states (see 
above) : "The choice of standards is a very important 
matter, for once they are taken all unknown glues are 
measured by them. Few published results of glue tests 
can be used for comparison, for seldom if ever have any 
two investigators worked on the same glue or glues, 
which have been described sometimes by their cost, 
sometimes by the stock from which they were manu- 
factured, and upon which only partial determinations 
were made. That definite standards will simplify and 
harmonize the grading of glue is self evident. 

"We arbitrarily fix sixteen nearly equidistant 
grades, and assign to them values running from 10 to 
160, allowing ten points between each grade. 

160 8013/ 8 

150 701/2 

140 601% 

130 A Extra 50 1% 

1201 Extra 40 1% 

1101 302 

1001 X 20 

90 VA X 10 

"Opposite these grades I have set the grades es- PETER COOPER 
tablished long ago by Peter Cooper, which are used GRADES. 
for comparison by many American manufacturers and 




The following determinations were made to es- 
tablish such definite figures on our standards as will 
enable anyone to pick out glues of the same character- 
istics. The higher standards, from 60 up, are neutral 
hide glues, clear, clean, well made, free from any odor 
of decomposition, and practically free from foam and 
grease, for the lower standards, bone glues were chos- 
en, because most low test glues show abnormal viscosi- 
ties. (The viscosities were taken in the apparatus 
described in Chapter VI, page 31. See original article 
Jerome Alexander Jour. Soc. Chem. Ind., 1906, 25, 158, 
for method. The jelly strength was taken as described 
in Chapter VII, page 37). 
































Fernbach states, relative to the grading of glues 
(Glues and Gelatines, 1907, page 57) : "A study of 
viscosities * * * of glues confirms what has already 
been said about the inadequacy of viscosity as the 
ultimate measure of glue strength. The author has 
tested more than thirty thousand samples of glue and 
gelatine, and relying invariably on the finger test (jelly 
strength) in preference to using any test machine. The 
results have always been concordant." 


In general, the operator in grading a sample must 
rely mainly upon the jelly strength, using other tests 
as auxiliary aids, and for comparison, must have in 
his possession samples of known grades with which to 
compare his unknown test sample. He will find in 
general that the jelly strengths and viscosities are 
comparable, or in other words, he might grade on the 
basis of either. If they do not check he should look " 

. - _ ... _ . . _ . . THE SAMPLE. 

upon the sample with much suspicion and inquire care- 
fully into the method of manufacture, quality of stock 
used, etc., before accepting the glue. In normal run 
glues, jelly strength and viscosity are the only tests 
absolutely needed. 

See also Frost and Linder (Proc. Am. Soc. Test. Mat., 1914, 
page 509). 



TESTS on joint strengths obtained with hide glue 
on a number of species showed that it was possible 
to glue them without obtaining glue failures in the 
test. The species tested, all of which gave successful 
results, were the following : 

Hard maple Douglas fir African mahogany THESE WOODS 

Yellow birch Red oak White mahogany GIVE STRONG 

Black walnut White oak Tanguile 

Red gum Central American Black cherry 
Yellow poplar mahogany 

Similar tests on greenheart were unsuccessful. 
Numerous attempts made to glue this wood failed in 
producing a strong joint. Similar tests made on 
maple coated with varnish, shellac, and airplane dope 
also failed to give good joints. The conclusion was 
that it was dangerous practice to try to glue over 
wood coated with these materials. It is, of course, pos- 
sible that special methods could be devised for doing 
such work if it was desirable. Similar tests using wood 
coated with lard oil, cylinder oil (mineral) and corn oil 
were made. The oils were rubbed into the wood with a 
cloth and the wood allowed to stand 15 hours before 
gluing. While no definite conclusion could be drawn, 
the results were surprisingly good. Specimens coated 
with all of these oils gave quite high strength values. 

Tests on plywood glued with animal glue and soaked EFFECT OF 
in gasoline and in engine oil indicated that these oils GASOLIXE ON 
did not have a deleterious effect on the glue joint over STRENGTH OF 
a period of 15 days. Subsequent tests over a period JOINTS. 
of 4 months showed some weakening effect. 

The common assertion that scratched surfaces make 
stronger glued joints than smooth surfacesjseems hard 
to prove. Comparative tests made on several occa- ' 

i i -r-m -r-k f * JOINTS VLRbUo 

sions by the Forest Products Laboratory all indicate SMOOTH . 
that the strengths of these two types of joints are prac- 
tically the same. 



The test specimens used by the laboratory were 

pairs of hard maple blocks, some with smooth and 

TOOTH PLANED some with tooth-planed contact surfaces. These blocks 

JOINTS ARE were glued with a high grade hide glue, allowed to 

NOT ADVISED. stand for a week, and then sheared apart in an Olson 

universal testing machine. Four joints of each type 

were compared in a single test. 

Eleven such tests gave the following average re- 


Scratched Joints 
Shear Wood Surface 
Test Strength in Failure 
No. Lbs. sq. in. Per cent. 
1 1787 25 
2 1366 

Smooth Joints 
Shear Wood Surface 
Strength in Failure 
Lbs. sq. in. Percent. 
3086 50 
1571 25 
2416 100 
1678 62 
2455 100 
2180 25 
2395 62 
2520 75 

2040 47 








Gen. Av'g 

It will be noted that in seven of the eleven tests 
smooth surfaces gave the better adhesion. Consequent- 
ly it would seem that there is no advantage in tooth- 
planing wood for gluing purposes. 

Some interesting points have been brought out on 
the gluing of laminated construction, particularly air- 
plane propellers, from recent experiments made at the 
Forest Products Laboratory at Madison, Wisconsin. 
HEATING WOOD Propellers had been found to give trouble with 
BEFORE GLUING open joints when made of certain kinds of wood, and 
GIVES STRONGER glued with certified hide glue. Propellers of oak and 
birch very frequently had open joints, while mahogany 
propellers could be satisfactorily glued even without 
heating the laminations. Heating the oak and birch 
laminations before gluing was found to give firm glue 
joints, and even in mahogany as well it was found that 



if the laminations were heated before gluing, the joints 
were more uniform in strength. All propellers in which 
the laminations were heated before gluing gave firm 
joints which showed no tendency to open up. 

Heating the laminations before gluing, however, 
was found to seriously retard the setting of the glue. 
Strength tests were made on large sized blocks glued 
up with hide glue to determine what effect heating 
laminations had on the glue strength. The tests were 
made about 10 days after gluing. The results obtained 
on this test are shown in the following table : 


8, 10 AND 12 HOURS.* 
Central American Mahogany. 

8 hrs. under Press. 10 hrs. under Press. 12 hrs. under Press. 

Max. Min. Av. Max. Min. Av. Max. Min. Av. 

Cold 2489 1251 1949 2418 1446 1995 2098 1280 1645 

Hot 1735 1250 1567 1845 1160 1589 1788 1390 1635 

Northern Red Oak 

8 hrs. under Press. 10 hrs. under Press. 12 hrs. under Press. 

Max. Min. Av. Max. Min. Av. Max. Min. Av. 

Cold 2489 1251 1949 2418 1446 1995 2096 1280 1646 

Hot 2001 1250 1659 2150 1362 1739 2220 1542 1910 

Hard Maple 

8 hrs. under Press. 10 hrs. under Press. 12 hrs. under Press. 

Max. Min. Av. Max. Min. Av. Max. Min. Av. 

Cold 3620 2367 3015 3170 1900 2751 3072 1815 2361 

Hot 3260 778 1652 3338 2124 2584 2960 2015 2576 

* Strength tests made 10 days after gluing. 

While, in all species the strength of the hide glue 
was fully developed in eight hours in cold blocks, in 
hot blocks the full glue strength was not developed in 
10 hours, and in oak even in 12 hours, an increase in 
strength being clearly shown for an increase in time 
under pressure. 

High density woods have been found to absorb 
heat faster and in greater quantities than low den- 
sity woods, so that mahogany showed less retarding 
effect on the glue than the oak and maple. 

Heating laminations has been shown to be desirable 
in order that open joints may be avoided, while at the 
same time the strength distribution becomes more uni- 
form. The retarded setting of the hide glue requires 




a longer pressure period to develop full strength, and 
under the conditions prevalent in glue rooms, a period 
of 12 hours under pressure is not long enough to de- 
velop the full strength of the glue. 

That there is a close relation between the viscosity 
and therefore the grade of animal glues, and their re- 
sistance to loss of strength in moist air, is strongly in- 
dicated in the following table, which gives the length 
of time different glues resisted a humidity of 98 per 

TE^T 1 









. 1.62 



' - Z 








. 2.00 
. 1.92 
. 2.90 
. 4.98 
. 4.14 
. 5.48 









14 % 












*In this test the specimens were kept at 90 per cent humidity 
for 120 hours (5 days). 
fThis is a vegetable glue. 

Specimens of V 8 -inch birch veneer were glued two- 
ply with the grain parallel, and with one square inch 
of glued surface. The specimens were suspended in 
a humidity chamber with a 1-pound weight hung on 
each, and the time required for failure of the glue joint 
was noted. Tests one and two were made at 98 per 
cent, humidity. In test three the specimens were kept 
at 90 per cent, humidity for 120 hours, when the hu- 
midity was raised to 98 per cent. No failure occurred 
at 90 per cent. The temperature was about 80 deg. 



A GLUE hydrometer is an instrument for meas- 
uring the density of glue solutions and ex- 
pressing the results in terms of the density of 
water, or in some scale such as Baume degrees THE GLUE 
that in effect also express results in terms of the HYDROMETER. 
density of water. Since the density of both glue solu- 
tions and water vary with temperature, hydrometer 
readings must take accurate account of temperature. 

The glue hydrometer usually employed consists of 
a copper pot and a hydrometer arranged for temper- 
ature of 75 C., or 167 F. The melted glue is poured 
into the copper receptacle and the hydrometer is al- 
lowed to sink until it finds its position. Some experts 
employ what is known as Weinhagen's Hydrometer. 
This is provided with a thermometric correction scale 
at the top of the instrument, and this is always clear 
of the liquid when the hydrometer is immersed. The 
temperature must be adjusted accurately before mak- 
ing the determination. 

This instrument is used to determine water ab- THE 
sorption. It is also used when inspecting glue rooms, HYDROMETER 
determining the amount of water and glue used by DOES NOT SHOW 
immersing the instrument into the glue solution in THE QUALITY 
the tanks, cookers or glue pots. This also affords a OP THE GLUE - 
very good check on the loss due to evaporation. This 
instrument cannot be used to determine glue quality, 
as its readings have no bearing whatever on viscosity 
or adhesiveness. 








DURING the war all the glue for use in air- 
craft construction was tested by the Bureau 
of Aircraft Production inspectors at the Forest 
Products Laboratory, Madison, Wis. More than 
a million pounds of hide glue furnished by ten differ- OYER ONE 
ent manufacturers had to be examined before its MILL ION 
shipment to the various aircraft factories was permit- POUNDS OF 
ted. This is not the first attempt which has been made GLUE INSPECTED 
to introduce standards in the glue trade, but it is the BY THESE 
first instance in which the majority of the large manu- METHODS. 
facturers, as well as many of the purchasers of glue, 
have recognized the same standards and assented to the 
validity of the same methods of testing. 

The methods which were adopted were selected as 
being those of rational basis, direct practical bearing, 
simplicity and convenience. They are not ideal ; a few 
of them are scarcely satisfactory. Nevertheless, when 
properly applied and interpreted, they will enable the 
chemist to select and grade glue. 

The physical constants of glues and glue solu- 
tions cannot be measured with the same precision as 
those of most of the materials which the chemist is 
called upon to test. Glue is a substance of widely 
varying chemical composition and physical condition. 
Tests made upon it are profoundly affected by factors 
which are difficult to control. Time, temperature, 
colloidal condition and the effects of micro-organisms 
are unusually important in glue testing. 

The methods which were adopted are as follows: 

For accurate work the viscosity, jelly strength and 
jelly melting point determinations should be made upon 
a sample which has been carefully dried at a low 
temperature to constant weight. The precaution, how- 
ever, is frequently disregarded. 

*From paper prepared by Wilbur Lloyd Jones, senior inspec- 
tor, B. A. P. 



Weigh out 50 grams of ground glue and add it to 
250 c. c. of cold water. Allow the mixture to stand for 
two or three hours in an ice box and keep the breaker 
containing the mixture covered with a watch glass. 
Then place the breaker in the water bath and raise the 
temperature gradually to 60 C., stirring every once in 
DETAILED a while. Keep the watch glass in place when the mixture 

METHOD FOB is not being stirred in order that the moisture which es- 
VISOOSITY. capes from the solution may be condensed. When the 
lumps have disappeared from the solution, recover the 
drops of condensed moisture on the watch glass and 
strain the solution through a piece of cheese cloth or 
wire gauze. Then cover once more with the watch 
glass and allow the solution to remain in the water 
bath until the temperature of the water in the annular 
ring of the viscosimeter is about 60 C. An Engler 
viscosimeter is used. Place a 200 c. c. viscosimeter 
flask underneath the orifice of the viscosimeter. Then 
pour the glue solution into the cup of the viscosimeter 
until it just covers each of the three level points, and 
adjust the thumb screws on the stand of the viscosi- 
meter so that the instrument is perfectly level. This 
should be done as quickly as possible in order that loss 
of moisture from the solution will be at a minimum. 
Then place the cover on the viscosimeter, insert the 
thermometer and regulate the temperature so that the 
glue solution in the cup is exactly 60 C., and the water 
in the jacket is somewhere between 60 and 61 C. Then 
remove the wooden plug with one hand and snap the 
stop watch with the other, and allow the glue solution 
to flow until the meniscus is exactly opposite the 
200 c. c. mark on the flask. Then snap the stop watch 
again and note the reading. The viscosity of the solu- 
tion is the number of seconds required for 200 c. c. of 
solution to flow at 60 C. through the standard orifice 
of the viscosimeter. Before making a second deter- 
minAtion, clean out the apparatus thoroughly and be 
sure that no glue remains in the orifice, nor on the 
wooden plug. The tests for odor, reaction, foam, jelly, 
melting point, and grease should be made on the residue 
left from the viscosity determination. 

The odor is determined by smelling the liquid. 


Take a piece of red and a piece of blue litmus and THE REACTION. 
dip both into the glue solution. Remove them and 
examine for change of color. If the blue litmus turns 
red or reddish, the solution is acidic. If the red litmus 
turns blue, the solution is alkaline. Glue solutions are 
usually either slightly acidic or neutral. 

The glue solution is then placed in a water bath FOAM. 
and heated to 60 C. It is agitated by a stirrer at- 
tached to a small electric motor for exactly one min- 
ute, after which time it is allowed to stand for ex- 
actly one minute. The height of the foam is then 

The residue is then warmed up once more in the GREASE. 
water bath and a small quantity of an aqueous solu- 
tion of a dye is added to it. A brush is then care- 
fully cleaned until it is free from every trace of 
grease. A test is made on the brush by dipping it 
into a small portion of a dye solution and painting a 
broad streak upon a clean sheet of unglazed white 
paper. If the colored streak is free from spots where 
the color has been repelled from the paper, the brush 
is sufficiently clean to proceed with the grease test. 
The brush is placed in the glue solution now colored 
with dye and several streaks are painted upon clean 
unglazed white paper, employing a moderate amount of 
glue solution in the brush each time. The number 
of "eyes" in the colored streaks indicates the amount of 
grease in the glue. (See pages 33 and 34.) 

The instrument which is in use at the Forest Pro- JELLY 
ducts Laboratory, Madison, Wisconsin, for determin- STRENGTH. 
ing the jelly strength of glues, is a modified form of 
an apparatus which is used for the same purpose 
in the laboratory of one of the large glue manufactur- 
ing companies. 

It is essentially a "float" which rests lightly on 
the surface of a jelly, and a "plunger," to which is 
attached a scale by means of which the depth of pen- A NEW METHOD 
etration, or rather, depression, can be measured. FOR JELLY 

The "float" is made of brass plate. It should not STRENGTH. 
weigh more than 200 grams. The bottom surface, 
which comes in contact with the jelly, should be rather 
large, in order to distribute the weight and to prevent 


the float itself from depressing the jelly to any appre- 
ciable extent. At the top of the "float" there is a 
guide of rectangular cross section through which the 
standard or scale of the "plunger" moves freely. An 
inverted trianguler section (1 c. m. in altitude) is cut 
away from the top of the front face of this guide, and 
the resulting diagonal line is divided into 10 equal parts 
in order to enable the operator to read the depression 
of the standard to tenths of a centimeter, and to esti- 
mate it to hundredths. 

THE PLUNGER. The nose of the "plunger" is hollow so that it can 
be filled with shot, and the weight of the plunger alter- 
ed at will. The hole through which the shot are added 
or withdrawn is closed with a screw. The standard is 
graduated in centimeters, and the zero mark on the 
standard is located at that point which is opposite the 
zero mark on the graduations on the "float" when the 
nose of the "plunger" is resting on a perfectly level 
surface. These details are explained in Fig. 17. 

This instrument, when used to test 12 to 1 jellies, 
has been found to be very delicate if the total weight 
of the "plunger" is 250 grams. To raise the weight 
of the "plunger" to this amount, a brass weight, a 
drawing of which will be found in the plan, will have 
to be placed on top of the nose. 

In making jelly tests, this apparatus is used as 
follows : 

Exactly 25 grams of ground glue are added to 300 
c. c. of cold water. The mixture is stirred, covered 
with a watch glass and allowed to stand in an ice 
box for two or three hours. At the end of this time 
the mixture is placed in a water bath and heated grad- 
ually to 60 C., stirring frequently but keeping the 
beaker covered with the watch glass to prevent evap- 
oration. When the solution is free from lumps, the 
condensed moisture is returned to the solution and the 
. glue is poured into a crystallizing dish of standard 
size and shape. A dish which is S 1 /^ inches in diameter 
and 2 inches deep will be found very convenient for 
this purpose. The depth of the layer of glue in the 
crystallizing dish should be exactly the same in every 
case. The crystallizing dish with its contents is then 










placed in an ice box at from 5 to 10 C., for 12 or 15 
hours. At the end of this time it is removed and the 
jelly strength of the glue is determined immediately. 
This is done by comparison. A sample of standard 
glue should be treated in exactly the same way as des- 
cribed above and at exactly the same time as the glue 
which is being studied. The glue being tested and the 
standard should be removed from the ice box at the 
same time and the jelly strength first determined by 
pressure with the fingers. Then the brass jelly tester 
should be employed and 3 or 4 readings of the amount 
of penetration determined. Obviously the weaker the 
jelly the greater will be the depth to which the plunger 
will penetrate. 

The depression of the 250-gram plunger against 
the resistance of the jelly is measured in millime- 
ters, and compared with the corresponding depres- 
sion of the plunger in the case of the standard glue. 
The consistency of the jelly is obviously inversely 
proportional to the depth of depression. This, of 
course, is true only in a more or less crude way; it 
is not an exact mathematical relationship. 

This test will be found to be as delicate, if, in- 
deed, not more so, than the so-called finger test. Jelly 
strength is expressed in percentages and it is equal to 
100 times the amount of penetration in the standard 
glue divided by the amount of penetration in the glue 
being tested. 

The jelly resulting from the above test is then 
allowed to stand uncovered in the laboratory at room 
temperature for 48 hours, at the end of which time 
the skin on the surface is broken and the odor of the 
jelly is noted. Even after 48 hours the odor should 
be sweet. 

To determine the melting point of a jelly the fol- 
lowing procedure is employed: A 12-inch length of 
6-millimeter glass tubing is bent in the middle so as 
to form a U-tube. 

A drop of hot glue solution (5 parts of water to 
1 of glue) is introduced into one arm of the U-tube. A 
stirring rod or a medicine dropper can be used con- 
veniently for this purpose. If a 12-to-l jelly were 


used a more sharply defined melting point might be 
obtained, but its behavior would be farther removed 
from the concentrated solutions which are used in 
gluing practice, and it would accordingly be of less DETAILS OF 
significance. When the drop of glue has sunk to a MELTIXG 
certain mark which has been etched half way down POINT ^ 
one side of the tube, the opening of the other arm 
is closed with the fore-finger, and the tube quickly 
plunged in ice water. The glue will now be found to 
be stationary, a cylinder of jelly exactly opposite 
a fixed mark on the tube. It is important that there 
should be no glue in any other part of the tube, be- 
cause it might clog the bore and subsequently prevent 
the free movement of the cylinder of glue. 

The U-tube with its cylinder of jelly is allowed 
to stand about an hour at 10 to 15 C. It is then 
immersed in a beaker of water (10 to 15 C.) to 
such a depth that the glue is beneath the level of the 
surface of the water. The temperature is then slowly 
raised and the water stirred constantly. The tube is 
fastened to a sensitive thermometer by means of rubber 
bands. At a certain definite temperature the cylinder 
of jelly will commence to slip from its position, sink- 
ing slowly at first. The temperature at which movement 
is first noticeable is taken as the melting point. The 
heat communicated from the walls of the tube melts the 
surface of the cylinder of jelly which is in contact with 
it, thereby allowing the jelly to fall of its own weight. 
Glue jelly is a very poor conductor of heat. Conse- 
quently, other methods which require the thermal 
penetration of a considerable mass of jelly will be 
handicapped on that account. 

The adhesive or strength test is carried out as 
follows : A piece of hard maple is cut into two ADHESIVENESS. 
halves of the size and shape indicated by the first 
specimen in Fig. 6. Dense, hard, straight-grained, 
thoroughly seasoned wood, free from defects, should 
be used. Preferably it should be flat-sawed lumber. 
The two blocks should be put through the planer and 
then over the jointer. The surfaces which are to be 
placed in contact should be absolutely flat, and they 
should fit perfectly. The moisture content should be 






between 6 and 13 per cent. It has been found unneces- 
sary to warm the test blocks above the temperature of 
the room. Moreover, it is undesirable, because even 
a moderate heating is liable to distort the blocks to a 
certain extent and prevent them from fitting together 

It is a good plan to test every unknown glue at four 
different water^glue ratios. With a moderately high 
grade glue, such as Peter Cooper's Standard No. 1, 
sets of specimens should be prepared, using 2, 2^4, 2 l /2 
and 234 parts of water respectively to one part of 
glue. It might be advisable in the case of an exceeding- 
ly high grade glue to prepare a test block at 3 to 1, 
and there are low grade glues which will give best 
results with less than 2 parts 6f water to 1 of glue. 

The glue solution should be used as soon as pos- 
sible after it has melted and attained a temperature 
of 140 to 150 F. The glue should be applied freely 
to both of the surfaces which are to be joined. It 
often helps considerably if the hot glue is brushed well 
into the wood, to assure proper penetration by the glue. 
The blocks should then be allowed to stand until the 
glue has thickened a little, but they should not stand 
long enough for the glue to "set." If the glue is 
touched from time to time by a finger which is rather 
quickly withdrawn, there will come a time when fibers 
or strings of glue an inch or two in length will be 
pulled up from the surface. When this point has been 
reached, the two blocks should be joined, rubbed to- 
gether slightly with light pressure, and then placed 
in a press designed in such a way as to assure an even- 
ly distributed pressure. As soon as possible the pres- 
sure should be applied. It should be a moderate pres- 
sure, just sufficient to bring the edges of the glued 
surfaces into approximate contact. It should be re- 
membered that for testing purposes it is better to em- 
ploy too little pressure than too much. 

By working rapidly one can prepare joints at four 
different concentrations for any glue, stack them in 
the press so that they will all be subjected to the same 
pressure, and finish the adjustment before the joint 
which was glued first has been "set." 


These joints should be left in the press for at 
least 15 hours. They may be then removed and placed 
in a drying rack, where they should remain for at 
least six additional days. At the end of that time 
they may be cut into shear blocks, as shown in Figs. 
5 and 6. 

These shear blocks are then tested in an Olsen 
Universal Testing Machine (Fig. 8), provided with 
a special shearing tool as shown in Fig. 7. The load 
should be applied at a rate not to exceed .025 inch 
per minute. A shearing strain is brought to bear 
on the layer of glue between the two wooden halves of 
the specimen. At a certain load each shear block will 
fail, and the failure will be either in the glue, in the 
wood, or in both. The load at which failure took 
place and the exact area of fracture are measured. The 
shearing stress in pounds per square inch can then be 

It is obvious that, whenever the failure occurred 
in the wood exclusively, the glue would have resisted 
a force somewhat greater than the one applied. It 
is only when the failure is in the glue entirely that 
its shearing strength has been fairly determined. It 
is more than probable that the higher the percentage 
the amount of failure in the wood assumes, the FAILURE HAS 
greater will be the disparity between the actual SIGNIFICANCE. 
strength of the glue and the load at which failure took 
place. A specimen which failed at 2,000 pounds per 
square inch, 90 per cent, of the fracture being in the 
wood, might indicate a stronger glue than one failed 
at 2,500 pounds per square inch where only 10 per 
cent, of the fracture was in the wood. 

Book II 




Book II 

CHAPTER XV Preparing the Wood for the Glue 

The Lumber Storage Test for Dryness Warming 

the Lumber Ideal Gluing Temperature 105 

CHAPTER XVI Preparation of Core Stock 

The Core Stock Free from Checks Crossbanding 
Allowing the Crossbanded Core to Dry Right and 
Wrong Sides Conditions Affecting Thickness 109 

CHAPTER XVII Preparing Glue for Use 

The Glue Mixer Soaking Glue Regarding "Cook- 
ing" The Glue Heater The Cleaning Vat^-Use of 
Pure Water Rainwater Soda in Water Use of a 
Glue Size Regarding the Changing of Brands 115 

CHAPTER XVIII Ideal Surface for Gluing 

Hardwoods End Grain Edge Gluing Concave 
Edges 123 

CHAPTER XIX Covering Capacity of Glue 

High Grade Glue Spread Costs Wastage Efficiency 127 

CHAPTER XX Glue Room Equipment 

Modern Appliances Kinds of Cauls To Prevent Glue 
from Sticking to Cauls 131 

CHAPTER XXI An Ideal Glue Room 

Ground Floor Location The Heaters Ventilation 
Drying Room Circulation of Air 135 

CHAPTER XXII Evolution of Glue Room Practice 

History Progress Unsolved Problems Conditions in 
Europe 141 


CHAPTER XXIII Glue and Finishing Departments 

Shifting of Responsibility Blisters Effect of Water 
on Veneers Loose Veneer An Example of Trouble 
Playing the Game Square 145 

CHAPTER XXIV Veneering Scroll Work 

Regarding Designs Elimination of Difficulties A 
Lesson for Beginners Thickness of Veneer. 149 

CHAPTER XXV Laying Fine Face Veneers 

Importance of Good Veneer The Redryer The Hot 
Box Taping Veneer Spreading the Glue Open 
Joints Use of Warm Cauls ... 153 

CHAPTER XXVI Spreading the Glue 

Evenness is Essential Intelligence Regarding Foam 
Good Glue is Necessary 161 

CHAPTER XXVII The Glue Salesman 

The Science of Salesmanship Know Your Line and 
Don't Knock the Other Fellow's Friendship Sales- 
Tests Enthusiasm Order Takers Competitors 
Service Kinds of Salesmen Advertising Form 
Letters and Trade Papers 165 

CHAPTER XXVIII Buying and Selling Glue 

Purchasing Department Quality vs. Price Requisi- 
tionsRecording Tests 175 

CHAPTER XXIX Paper Box Adhesives 

Selection of Glue Box Making Machines Silicate of 
Soda ... . 179 

CHAPTER XXX Avoid Abuses 

Good Glue Glue Room Temperature Weighing 
Boiling of Water Correct Temperature Melting 
Freezing Co-operation 181 



TO obtain the best results in the glue room it is not 
enough that the glue be properly, prepared for 
the wood; it is equally necessary to have the THE LUMBER 
wood properly prepared for the glue. This prepara- SHOULD BE 
tion should commence early in the process of making PREPARED 
lumber as far back as the time when the tree 
is cut down in the forest. Trees should preferably be 
cut during the late fall and winter months, for at this 
time the trees are dormant and fairly free from sap. If 
the tree is cut down during the spring or summer 
months when it is in the growing stage the wood is 
very susceptible to atmospheric changes; and the con- 
tinual expanding and contracting of the wood is very 
detrimental to the life of a glue joint. Much of this dif- 
ficulty may be overcome by allowing the lumber to dry 
or season for several years. However, long air season- 
ing is no longer feasible, and kiln drying is usually re- 
sorted to. 

Every factory should have a place for storing lum- 
ber between the dry-kiln and the workshop. This 
storehouse should be well ventilated so that the air will STORED AFTER 
be occasionally changed fresh air entering from the LEAVING 
outside; which will give it the right humidity. The KILN 
lumber should be made quite dry in the dry-kiln before 
being placed in this storehouse, which should be kept 
at a temperature of about 60 degrees Fahrenheit, 
which temperature, together with the humidity in a 
properly ventilated place, will enable the lumber to so 
adjust itself that it will become less changeable in its 
nature and less prone to yield to atmospheric influ- 
ences, and, therefore, more dependable after it is 
worked up. 

In order to save extra handling of the lumber, 
tracks should be laid in the storehouse so that it may 
receive the loaded cars direct from the dry-kiln; and 
then in turn send them to the cutting-out department 






without any changes. If this cannot be done the lum- 
ber must be piled with strips between each layer the 
same as when piling for the dry-kiln. 

Lumber should always be tested for dryness before 
being glued up. If unfit stock be worked up it will 
never be made right and will always be a source of 

A method of testing lumber for moisture by no 
means uncommon is by carefully measuring the width, 
then heating it in an oven or hot-box and noting the 
amount of shrinkage. But this is not a safe test. The 
better method is to weigh a small piece on a very sensi- 
tive scale ; and after heating in an oven at about 215 
F., for twenty-four hours, note the change in weight. 
Before weighing the second time the board should be 
allowed to cool to the same temperature as when it was 
first weighed. Heating in the oven should eliminate the 
last particle of moisture and the difference in weight 
before and after heating should give the percentage of 
moisture which the lumber contains. 

Lumber should never be glued up when cold, 
whether it be edge jointing or veneering; and whether 
it be animal or vegetable glue that is to be used, it will 
be safer to warm the wood if it is cold. This is due to 
the fact that the cold glue solution, or one that is 
chilled by cold wood, is too viscuous to permit the glue 
to enter the pores and obtain a hold. However, care 
must be taken not to overdo the heating. The best re- 
sults are obtained between 80 F. and 95 F. 

All things must work in harmony in order to pro- 
duce the best results, and the temperature of the room 
in which the work is done must be in harmony with 
the required temperature of the wood, as well as the 
temperature of the glue. There was a time when a 
great many people had the idea that the higher the 
temperature of the glue-room the better; with the 
result that the temperature was such as to be detri- 
mental to the health of the workmen. All this was in 
harmony with the other mistaken idea that glue itself 
had to be prepared and used at a high temperature. 
But careful experiments show that a temperature suit- 


able for the workmen is suitable for the work. Such a 
temperature is from 70 degrees to 75 degrees Fahren- 
heit. While this temperature is sufficiently high, under AN AVERAGE 
no circumstances should the glue be used at a lower TEMPERATURE 
temperature. It is not enough to have the glue hot and 
wood warm, because the cold air will chill the outer 
surface of the spread and impair its power of adhesion. 

The temperature here indicated is the one to be 
maintained at the point of contact between the air and 
the glue. For this reason the thermometer should be 
on a level with the glue spreader and veneer-laying 
bench. A few feet in height frequently makes a differ- 
ence of several degrees in the temperature of the air, 
especially during the period of early morning heating 
before the warm air has been diffused uniformly 
through the whole room. For this reason, if the ter- 
mometer is placed higher than the point of contact be- 
tween the air and the glue, one is liable to begin opera- 
tions in a temperature several degrees lower than that 
required, thereby injuring the work without know- 
ing it. 

With the temperature of the air at 75 degrees Fahr- 
enheit, the wood at 95 degrees and the glue at 140 de- IDEAL 
grees, we have that ideal combination which, every- GLUING 
thing else being equal, will insure the best possible COMBINATION 



IN the process of building up reinforced wood bodies 
for pianos, furniture, automobiles and interior 
trim there is what is called a "core," or center ; the 
proper preparation of which is of great importance to 
the finished article. This center, being the foundation 
of the structure, must be right ; otherwise the quality 
of the finished article will be defective. It has been THE CORE 
thought by some that the core being covered by outer 
layers requires little attention, as all defects in mate- 
rial and workmanship are hidden from view, and will 
never be revealed, but a greater fallacy can scarcely be 
conceived. Of course, this core does not require the 
same high quality of material that is needed for the 
outer, or face layer; but the contention that anything 
is good enough for corestock is the one we wish to 

Core stock should be sound, and may be of almost 
any kind of wood grown on this continent ; the kind to 
be used depending entirely on the use to which the 
finished article is to be put. Because of its strength 
and shock-resisting powers Sitka spruce is used for 
airplane work ; while in the manufacture of furniture 
and pianos the wood selected is usually such as will 
approximately match the texture of the veneer or 
crossbanding with which it is to be united; although 
quite frequently cost is the prime factor in determin- 
ing the kind of wood used for this purpose. But less 
depends on the variety of wood than on its preparation 
for the work in hand. 

When we say that wood for core stock should be 
sound we mean free from checks of various kinds. CORE ST 
There is a great deal of wormy chestnut used for this SHOULD E] 
purpose, and to this there is no serious objection un- 
less it is so badly eaten as to destroy the surface for 
the glue ; and this is hardly conceivable. 

Only one variety of wood should be used in each 






core. If two kinds of wood are glued together in one 
core, say, basswood and birch, there is sure to be 
trouble which may not show itself until after the goods 
are finished. The swelling of these two woods as a re- 
sult of the action of the moisture from the glue will 
not be in unison; neither will the shrinking be uni- 
form ; and an uneven surface will result in consequence. 

After the core stock has been glued up it should be 
sent to the drying room in order that the joints, which 
have swollen from the action of the water in the glue, 
may shrink back to their normal position. If they are 
not allowed to dry out properly before being planed 
there will be more than the proper amount of fiber re- 
moved from the swollen joint, with the result that 
when the joint has dried out it will have shrunken be- 
low the level of the surrounding wood; and the 
depression thus made will show after the stock is fin- 
ished, unless a very heavy crossband has been used. 

For the better grade of work core stock is always 
crossbanded. This crossband consists of a sheet of 
wood glued on each side of the core, with the grain of 
the one running crosswise of the grain of the other; 
the object being to reinforce it to prevent checking, 
twisting or warping. It is the practice in some shops 
to lay this crossbanding at the same time that the face 
veneer is laid ; but this plan is not here recommended, 
nor is it followed in the best shops. The plan adopted 
by those who have the best quality of work in view is to 
lay the crossbanding by itself and, after taking from 
the press, pile it away in the drying room with strips 
between each piece to dry out before laying the face 

Laying the crossbanding in advance of the face 
veneer has several distinct advantages over the laying 
of both at the one time; chief of which is the better 
opportunity it affords of properly preparing the sur- 
face for the face veneer. Fine face veneer is usually 
cut very thin, and any unevennes in the surface to 
which it is glued will be reffected through it after the 
stock is finished, and will detract considerably from 
the quality of the goods as well as add to the cost 01 


finishing. Crossbanding, on the other hand, is usually 
cut much heavier than veneer intended for face work, 
and is rotary cut ; that is, it is sliced, or peeled off the 
outside of the log as the latter is revolving in a lathe. 
The method of cutting crossbanding makes it difficult 
to get a surface sufficiently smooth for fine face veneer 
without some cleaning up; and this cleaning up can 
best be done after the crossbanding has been fastened 
to the core. 

Allow the crossbanded cere to remain in the drying 
room a sufficient length of time to become properly dry 
before doing anything toward cleaning it up ; other- ALLOW THE 
wise there is danger of weakening the glue-joint. The CROSSBANDED 
length of time required for this will depend on the c< 
capacity of the drying room; but in a room such as 
that described elsewhere in this book, from three to 
four days will be sufficient to eliminate all danger of 
the cleaning-up process affecting the glue joint; and 
render it sufficiently dry to receive the face veneer. 

This cleaning-up is usually done by putting the 
stock through the sander. If the surface is in pretty 
bad shape, use two or more drums, with coarse paper 
on each ; no fine paper being used for this operation. It 
is better to use more than one drum for cleaning up, 
taking shallow cuts, rather than one drum and a deep 
cut, as the shallow cuts are less apt to affect the glue by 

It is very important to have the crossbanding 
thoroughly dry before it is laid. There are some who 
have the idea that, while it may be important to have 
the face veneer dry, the condition of the crossbanding DRY 
is not a matter for any concern. These people have 
their troubles in consequence of their neglect in this 
connection; but they ascribe the cause to something 
else, and consequently they never find it, and, there- 
fore, do not remedy it. The writer has seen face veneer 
broken across the grain in consequence of being laid on 
crossbanding which has not been properly dried before 
it is laid. It was %-in. crossbanding and had checked 
in the process of drying after the face had been laid; 
and at the point of these checks it had exerted sufficient 










force to rupture the face veneer above. 

What we have said about the importance of using 
only one variety of wood in a core applies with equal, 
if not greater, force, to the use of crossbanding ; for 
the nearer our work brings us to the point where the 
face veneer is to be laid, the more the necessity for 
care. If one has a lot of odds and ends of stock of vari- 
ous woods that he wishes to use up, it may be done by 
sorting the lot over and separating each kind of wood ; 
and if there is a difference in thickness, separating 
these, too. These should then be dried and cut to re- 
quired size, then taped ready for use. 

There is always a right and wrong side to rotary 
cut stock; and the thicker the stock, the more pro- 
nounced is this distinction. The right side of the -stock 
is that which was on the outside of the log during the 
process of cutting; and the wrong side is that which 
was the inside of the sheet as it was peeled off the log. 
To illustrate. Take a long, narrow piece of paper and 
bend it in a circle. The outer side of this circle of paper 
corresponds to the right side of the crossbanding, and 
the inner side to the wrong side as it leaves the log. 
Now straighten the paper out and note closely in your 
mind what follows. Imagine the paper to be %-in. 
more or less thick, and see the strain there is on the 
inside as we straighten it out. The strain is more than 
the fibers can withstand ; and they break and separate. 
This side with the ruptured grain and fiber is the 
wrong side of the stock. 

The crossbanding should always be laid with the 
right side out the wrong side being as far from the 
face veneer as possible. The right side is much more 
easily cleaned up ; and what is more, if the wrong side 
were left up, the ruptured fibers and resultant scales 
would be so affected by moisture from the glue and 
subsequent atmospheric changes that they would im- 
part a corrugated appearance to the face veneer. 

The right side of crossbanding is the side to be 
taped, so that the tape will be removed when cleaning 
up for the face veneer. But this applies only to cross- 
banding that is laid in advance of the face veneer. If 


the crossbanding and face veneer are to be laid at the 
one time the wrong side of the stock is the side which, 
in this case, should be taped, in order that it may be 
laid next to the core and as far from the face veneer as 
possible. The joint between the tape and the wood is 
not as firm and strong as a glue joint between two 
pieces of wood made under pressure. There is always 
danger of the tape coming loose hence the reason 
for having it laid as far as possible from the face 

As before intimated, crossbanding is cut in various 
thicknesses ; the thickness to be used to be determined 
by the nature of the work in hand. Crossbanding is 
done to add strength to reinforce the thing cross- 
banded; and unless the crossbanding is of a suitable 
thickness to match the core it will be a source of weak- 
ness and not of strength. 

If one is making thin panel stock to be made five- 
ply, in the very nature of things everything must be 
thin probably Va-in. core with 1/20-in. crossbanding 
and 1/30-in. face. But if one is making a heavy buffet 
top and crossbanded it with 1/20-in. stock he would 
very likely be building into it trouble for the future. 
Such thin crossbanding would not be a source of THICKNESS 
strength to a heavy top that needed to be reinforced ; OF THE 
and if not a source of strength, then it becomes a dan- CORE STOCK 
gerous source of weakness. Should such a core have a 
tendency to warp, such a thin crossbanding would be 
more likely to break under the strain imposed than to 
offer any effective resistance ; and if this happened, the 
last state of the top would be worse than the first. 
Nothing less than i/s-in. stock should be used for cross- 
banding l^-in. core; decreasing or increasing in 
thickness as the requirements of the core demand. 



THE task of preparing the glue required for the 
day's work should never be entrusted to a novice, 
but to a person of high intelligence and long 
experience. Much depends on how this work is done 
a mistake at this end of the line may prove disastrous 
to the whole output of the day. 

While a person of experience is preferred in the 
preparation of glue for use, any man of good intelli- 
gence with experience in its use can soon grasp the 
essential points and become proficient at the work. 
But it cannot be done in an hour, nor in a day, and for 
this reason every glue room should have an understudy 
who is qualified to take the place of the head glue mixer 
in the event of the latter being off duty. 

There is a difference of opinion regarding the ques- 
tion of soaking glue in cold water before heating it for 
use. Our modern glue-mixers have made it possible to 
reduce glue to the liquid state in a comparatively short 
time without previous soaking; at the same time the 
writer favors soaking first where this can be done 
without deterioration of the glue, as it is not good for 
the glue while in the dry state to be plunged into hot 
water, or even into a hot glue solution. But if the glue 
is put into the dissolver with cold, or even lukewarm 
water, and the temperature of the whole raised gradu- 
ally, no injurious effects will result, and previous soak- 
ing is, therefore, unnecessary. 

Much glue is injured in the process of soaking, 
especially in hot weather. It is put to soak too far in 
advance of requirements the process of decomposition GLUE IS 
sets in before it reaches the heater. If the glue can be INJURED 
kept at a low temperature while soaking, no bad effects IN* SOAKING 
will result from soaking over night, or even a few 
hours longer. If one has more glue soaking than will 
be required for the first three or four hours' work it 
would be much better to leave it in the cold soak than to 




put it in the hot heater, which would hasten the process 
of decomposition. Glue that is kept in the soak may be 
added to the heater at intervals as required; but it 
would be better to always empty the heater before add- 
ing fresh glue. The reason for this is : Heat deterior- 
ates glue, and the process of deterioration begins soon 
after a certain temperature has been reached. The 
change is very slight at first, nevertheless there is a 
change ; and if we add fresh glue with some of the old 
remaining, the deteriorating effect of the heat on the 
old glue is increasing until, by the end of the day, that 
which remains of the early morning lot has decreased 
in strength probably 50 per cent. I do not mean that all 
the glue in the heater has deteriorated to that extent 
only the original lot, which, being mixed with fresh 

FIG. 18 


glue, has saved itself from being rendered practically 
useless for permanent work; but saved itself at the 
expense of the glue that was added from time to time 
by distributing itself throughout the whole. 

There is always an advantage in having glue soaked 
ready for the heater, as, in case of emergency, one can 
prepare it in a very short time and more easily regu- 
late the supply for the day's requirements. And where 
one must soak the glue, some method for keeping it 
cool and prevent a lessening of its quality should be 
adopted. For this purpose a cupboard with shelves 
(Figure 18) on each of which is placed a coil of water- 
pipes with cold water running through them and on 
which the pans of soaking glue are placed, will keep 
the glue at a sufficiently low temperature to prevent 
injury within a reasonable time. The water which 
runs through these pipes need not be wasted, as it can 
be turned into the reservoir and saved for boiler 

The idea that glue must be "cooked" before it is "COOKING" is 
ready for use has long since been exploded. Time was UNNECESSARY 
when men thought that glue would not hold unless it 
was heated to the boiling point and kept there for 
some time all the way from one to three hours. And 
this was done, all unconscious of the fact that each 
minute of sustained heat was eating at the very life of 
the glue and lessening its adhesive qualities. In those 
days men talked of glue "cookers ;" but with the pass- 
ing of the cooking idea there passed away also the 
words which gave the idea expression; and in their 
place have come the words "heater" and "dissolver," 
which signify just what they are expected to do. 

While one must not cook animal glue in preparing 
it for use, it must not be used cold or at too low a tem- 
perature. There is a tendency on the part of some peo- 
ple to rush to the other extreme when the danger of A TH ERMOME- 
one extreme is pointed out to them. Some have rea- TER is 
soned that if heat injures glue, then the proper way to NECESSARY 
use it is cold ; and they have tried to do this, but with 
disastrous results. The proper temperature at which to 
use glue to obtain best results is 140 to 150 degrees 





Fahrenheit : and as soon as it reaches this temperature 
it is ready for use. Every glue heater should be 
equipped with a thermometer for registering the tem- 
perature of the solution. No matter what else one has 
or has not, a thermometer should be considered an in- 
dispensable part of the glue room equipment. 

As a preliminary to each day's operations the 
greatest care should be exercised the evening before in 
cleaning up all the glue room utensils. If these are not 
kept clean, tire stale glue adhering to them will become 
mixed with the day's preparation and set up a deterio- 
rating influence. For this purpose a vat, of the 
required size, filled with water into which the utensils 
may be placed to soak away the old glue, will be of 
great advantage; then in the morning they may be 
rinsed clean with clear water, which will take but a 
few moments. The vat should have a drain pipe at the 
bottom with a valve to facilitate cleaning, and should 
be emptied and refilled each day, otherwise it will soon 
become foul and offensive. 

Every glue room operator should contribute his 
share toward making working conditions as pleasant 
as possible. The glue room may be made a pleasant 
place in which to work if ordinary care is exercised, 
but if neglected it is liable to reach the opposite ex- 
treme. If the floors, benches and machines are kept 
clean from the start they will give very little trouble, 
as but little time is required to keep them clean if they 
are cleaned daily. But if they are allowed to go on for 
days, and sometimes weeks and months, daily accumu- 
lating fresh coats of glue, the condition will soon be- 
come such that no man with any regard for his per- 
sonal comfort or any knowledge of the rules of health 
would remain in the room longer than would be abso- 
lutely necessary. The benches should be scraped and 
the floor washed with hot water. A few minutes the 
last thing before leaving at night will make everything 
clean and sweet and put the room in such shape that 
one will not dread to enter it in the morning. 

The careful and economical glue mixer will keep in 
touch with the progress of the work in the gluing-up 



department in order to know how much glue to keep in 
course of preparation, and not have any left over at the 
end of the day. In warm weather glue that has been 
left over from the day before will seldom be fit for use 
and is usually thrown away. There is a great quantity 
of glue wasted in this way, and it ought not to be. 
With glue soaked ready for heating, it would be a very 
small matter to prepare an additional lot, should the 
day's supply run out before the day is done, and there 
need be no hold-up of the work or time wasted. In view 
of this there is no excuse for having a quantity left 
over to be thrown away and wasted. 

Decomposition of glue is frequently hastened by the USE PU8E 
water with which it is mixed. If this water contains WATER 
organic impurities, the process of decay will com- 
mence as soon as the water and glue come together. 
The value of glue may easily be reduced one-half by the 
use of impure water. 

There are many things to be found in water which 
will injure glue. Water drawn from extremely deep RAIN WATER 
wells, as well as river water which flows over a lime- 1S GOOD 
stone bed, will frequently contain a sufficient quantity 
of lime or iron or other chemicals to seriously injure 
the glue. Some concerns that use a large quantity of 
glue have found the ordinary sources of water such a 
menace to their glue that they adopted the use of dis- 
tilled water for mixing purposes. Water from the 
boiler, or water into which steam from the boiler has 
been condensed ought not to be used for mixing glue. 
Most boiler compounds are injurious to glue, and con- 
densed steam from the engine is most certain to con- 
tain a quantity of grease or oil. Where it can be ob- 
tained, clean, fresh rain water should be used for mix- 
ing glue; or if this is not obtainable, some means 
should be adopted for purifying the water, either by 
filtering or distillation. 

Water containing an excess of lime may be purified 
by adding one-half pound of ordinary washing soda to 
a thousand gallons of the water. The effect of the 
chemical action produced by the soda will be the pre- S( DA WILL 
cipitation of the impurities to the bottom of the ves- P 







sel. But one must be careful and not use the soda in a 
larger proportion than the above, as washing soda is 
an alkali, which, in certain proportions, would be in- 
jurious to the glue, and the last state would then be no 
better than the first. 

It is very difficult, except in the open country, to 
obtain rain water that is not impregnated w r ith impuri- 
ties, such as soot, etc., gathered from the air in its de- 
scent to earth. Such impurities may be removed by 
filtering the water through charcoal. Place several lay- 
ers of burlap in the bottom of a barrel or tank, over 
which place a foot or so of powdered charcoal, and let 
the water filter through this. The tank should be 
cleaned out at intervals, the length of which must be 
determined by the condition and quantity of water to 
be filtered. 

The proper preparation of glue for the wood-work- 
ing plant requires considerable knowledge; especially 
is this so in the preparation of glue for the veneer 
room. One must know the kind of glue he is using, also 
the kind of wood on which it is to be used. Different 
glues require a different percentage of water in their 
preparation, and different woods require a glue solu- 
tion of a different consistency. Hard, close-grained 
woods, such as maple and birch, do not require as 
heavy a glue solution as basswood or poplar, which, 
while close-grained, are soft and absorbent and will 
imbibe a lot of glue ; nor yet as heavy a solution as oak, 
which, while hard, is very porous and will absorb a 
large quantity also. 

Where one has to prepare a glue solution for one 
kind of wood, say, a hard wood or a soft wood, it is a 
comparatively easy matter ; but where one is called on 
to prepare a solution to meet the requirements of two ; 
the problem is perplexing, as one cannot have a thin 
and a thick glue both in the one solution. But the glue 
room is sometimes expected to do more than its share ; 
and this is one of the instances. As a matter of fact, 
one cannot prepare a glue solution that will meet the 
requirements of the two extremes of hard and soft 
woods unless these two woods will come part way and 



partially meet the requirements of the glue. This diffi- 
culty is probably met with in the preparation of glue 
for the veneer room more frequently than anywhere 

As before said, where two kinds of woods are to be 
glued together, both glue and wood must go part way A PROBLEM 
to meet the requirements of the other. Suppose we are SOLVED 
laying a poplar crossbanding on a maple core. Here is 
a case where the core requires a thin glue and the 
veneer a comparatively heavy glue. In a case of this 
kind we will have to prepare the glue to meet the re- 
quirements of one of the woods, and prepare the other 
wood to meet the requirements of the glue. In this 
case the correct plan would be to prepare the glue to 
meet the needs of the soft veneer ; and prepare the hard 
marie core to meet the glue. This can be done by pre- 
paring a heavy glue solution for the veneer and rais- 
ing the fibers of the hard core by sanding with coarse 

But let us reverse the situation and bring out a lot USING A 
of hard veneer to be laid on whitewood or basswood GLUE SIZE 
cores. For obvious reasons we cannot machine sand 
the veneer as we did the hard core in the other 
instance, and the process of hand sanding is too slow 
and expensive to be considered; so we will have to 
again prepare the glue to meet the requirements of the 
veneer, only it must be made thin this time, and face 
the problem of how to prepare the soft core to meet the 
requirements of the glue. The problem thus presented 
is solved by glue-sizing the soft core with a thin glue 
solution ; thus sealing up the pores and neutralizing its 
absorbant qualities. This glue-size should become 
quite dry before the gluing-up process begins. 

The proportion of glue and water to be used in pre- 
paring the glue solution for any wood is determined as 
much by the kind and quality of the glue as by the 
wood on which it is to be used usually, if not always, 
the proportion of water increasing with an increase in THE GLUE 
the quality of the glue. And in the preparation of glue SHOULD BE 
there should be no guesswork. The strength of the WEIGHED 
glue should be known as well as the requirements of 


the wood on which it is to be used ; and the glue should 
be weighed and the water measured. I wish to empha- 
size the importance of weighing the glue, because in 
the minds of some, it is so much easier to measure glue 
than it is to weigh it; and they follow the course of 
least resistance. But a bushel of glue does not always 
weigh the same that is, one bushel of glue may weigh 
several pounds more or less than another bushel of 
even the same grade of glue the weight depending 
largely on the condition of the glue. A finely ground 
glue will rest more compactly in the measure than 
would be the case with coarse, flake, shell or cake glue, 
and, therefore, weigh more ; the weight increasing 
with the fineness. 

After one has ascertained the requirements of any 
given wood, as well as the proper glue solution to meet 
these requirements, he should make a memorandum of 
the facts and preserve the data for future reference; 
as it is not safe to trust to memory in a matter of such 
importance. This memorandum should contain all the 
known facts concerning the glue ; including the result 
of all tests, if tests of a specific nature have been made. 
The great range in the quality of different glues 
makes it inadvisable to frequently change the make 
unless one has a well equipped laboratory for testing 
the article. Even then the practice is a questionable 
one from an economical standpoint. When one has a 
glue made by a reliable concern that has met the 
requirements of the past there should be some greater 
BE CAREFUL reason than a mere desire to try some other kind be- 
IN CHANGING fore & change is made. If one has a laboratory for 
thoroughly testing glue it would be well to be always on 
the lookout for something' better and cheaper; and 
whether a proposition to change glue is advisable or 
not can be ascertained by testing a sample. But where 
there is no proper equipment for testing glue, the glue 
room operator is placed at a disadvantage each time a 
change is made, in that he must learn his glue all over 
again ; and perhaps spoil considerable work before he 
understands it. 



E fact that there is such a thing as an ideal sur- 
face for gluing or one that is more likely to make 
a permanent job than another, has been recog- 
nized as far back as the time when all woodworking 
was done by hand ; for in those days the wood-worker 
had his toothing plane with which he made very fine 
grooves in the wood for the purpose of removing the 
smooth, polished surface made by the hand plane in the THE GLUE 
process of cleaning up the surface preparatory to the SURFACE 
gluing and laying of the veneer. Good glue will retain 
its hold for some considerable time on any good, clean 
surface; but where one desires a glue joint that will 
be permanent, and one that will outlive the maker, he 
should give special care to the preparation. The proper 
preparation of a surface for gluing is a comparatively 
easy matter today, because of increased facilities for 
doing the work. It is pretty generally recognized and 
admitted that the ideal surface is one that is perfectly 
level and on which the fibers of the wood are suffici- 
ently loose to allow the glue to penetrate and secure a 
firm hold ; at the same time not sufficiently so to allow 
the glue to accumulate in quantity and prevent any 
surplus squeezing out. 

In preparing such woods as maple and birch, and 
other hard, close-grained woods, the drum sander, with 
but one drum fitted with coarse paper, will prepare a 

_._ . - . 11* i -TI i HARD WOODS 

surface which, everything else being equal, will make a 
glue joint that will last away beyond the lifetime of the 
man who did the work. 

It may not always be convenient to use the drum 
sander for the purpose of preparing corestock for glu- 
ing; then the scraping machine may be used for the 
purpose. In fact, for some woods the scraper is prefer- 
able to the sander. For instance, such woods as oak or 
chestnut, which have hard and soft places, the sander 
is liable to press deeper into the soft places than into 







the hard; and an uneven surface will be the result. 
With the scraper it is different, as the cut will be uni- 
form over the hard and soft places. A special blade for 
this work is now made by some manufacturers of 

Difficulty is frequently experienced in making a 
glue joint on end wood, or in gluing the grain side of 
one piece to the end wood of another. The cause of the 
difficulty is usually in the end wood, which absorbs all 
the glue. Or in cleaning up the end wood it may be 
polished too smooth; or in cutting, the saw may have 
burned it smooth and hard, which is likely to be the 
case with a hard wood like maple and birch and some- 
times even walnut. In this latter case the remedy is to 
remove the hard surface with sandpaper, rubbing suf- 
ficiently to merely break the polish. 

If the end wood is open-grained or otherwise of an 
absorbing nature it would be well to glue-size it to seal 
up the pores, using a thin glue for the purpose. This is 
advisable on such woods as basswood and poplar and 
even oak. 

The preparation of the glue joint between boards 
for building up corestock, or for other purposes, is 
equally as important as that for veneering. Here, as 
elsewhere, to insure a permanent joint the surface 
should not be smooth and hard. A good glue joint, that 
is, one made with a high grade glue and with the sur- 
face of the wood in an ideal condition, should never 
open under normal conditions. Of course, if a glue 
joint becomes soaked with water, unless it is a water- 
proof glue, it will open. But under what we may call 
the average condition the wood will break before the 
glue will give way. 

In addition to the proper preparation of the surface 
the edges of the pieces to be glued should not be made 
perfectly straight, but should be made slightly hollow 
to insure permanency. The writer was once consulted 
regarding the cause of open joints and on investigation 
found that the joints were being made slightly rounded 
that is, the boards were made slightly wider in the 
center than at the ends. The object being to facilitate 


clamping up, as only one clamp on each end of a four- 
foot board was being used; the argument being that 
there was sufficient spring in the center of the rounded 
board to take the place of clamps. 

But the man who conceived the idea of gluing up 
stock in this manner had overlooked a very important 
factor in determining the quality of the joint, and that 
is, the spring supplied to the center as a result of the ACTg BOTH 
rounded edge of the board was a permanent force, and WAY8 
one which operated two ways ; for while it gave press- 
ure to the center when clamping up, it was forcing the 
joint apart at the ends when the clamps were removed. 
This force, together with the fact that the ends of a 
glue joint always dry out more rapidly than the parts 
farther in and which creates a strain on the ends which 
dry out first, was sufficient to draw the joints apart; in 
some instances breaking the wood in the immediate 
vicinity of the joint. 

An ideal edge for gluing up is one that is slightly 
hollow or concave; that is, when the two edges are 
placed together they will meet at the ends only, gradu- 
ally and slowly separating toward the center. This 
requires more force and more clamps to bring the 
edges together than is the case with the rounded edge ; 
and although the spring or force resulting from the NCAVE 
concave edges is a permanent one, it is evenly dis- EDGE Zl 
tributed from the center to the end, and is so located 
that it is comparatively harmless. In any event, the 
strain is in the center and far away from the ends, 
where glue joints usually open. Not only that, but it 
is a positive help to the ends, as it increases the pres- 
sure of each piece toward each other at these points 
instead of away from each other, which tends to 


EVERY manufacturer, regardless of line, is inter- 
ested in the covering capacity of the glue, for it 
is this point, all other factors considered, that 
determines the cost of the glue. We know that high- 
grade glues will take more water than low grade; on 
the other hand, high-grade glues would prove too ex- 
pensive for certain purposes, as, for instance in the HIGH GRADE 
manufacture of paper boxes. Again, one would not GLUES SET 
use high-grade glues in veneering, regardless of cost, T QUICKLY 
because they set too quickly. We know that liquids hav- FOR VENEERING 
ing the same specific gravity will cover the same 
amount of surface. Also, as has been previously ex- 
plained that glues can be prepared to give the same 
viscosity tests (varying proportions of water and 
glue) , hence, the liquids being the same, they will cover 
the same amount of square surface. 

The following table was published in Glue, June 
number, 1911. 




Yield of Liquid Glue Covering in 

Glue Grade. per 1 Ib. Dry Square feet. 

A Extra ........................ 3.65 79 

1 Extra ......... _ ............. 3.45 75 

1 ....................... _ ........... 3.34 72 

IX .................................. 3.08 67 COVERING 

- 2.94 64 CAPACITY 

1% ....................... _ ....... 2.82 61 

1% ................................ 2.68 58 

1% ................................ 2.55 55 

1% ................................ 2.43 53 

1% ................... - ........... 2.31 50 

2 .................................... 2.19 47 

It is to be regretted that glue prices have been so 
uncertain, and will likely be so for some time to come 
that we cannot cite a correct example as to possible 
savings, however, one can easily figure differences in 





the spread costs from the figures given in the table. 
For example, A Extra will with 1 Ib. dry glue cover 
nearly 70 per cent more surface than can be covered 
with 1 Ib. dry glue of the grade No. 2. 

The writer has always advised his clients to deter- 
mine the cost of spread from the cost records. The 
cost scheme should show the number of square feet 
covered in your veneering, joint, or to whatever line or 
use your glue has been applied. You know or should 
know the amount of glue used, and this will give the 
spread cost. Having established a fairly accurate 
amount, use this glue as a standard in future spread 
tests or comparisons. This can be done in a fairly safe 
measure by comparing viscosities. 

Someone may ask the question, "Why not deter- 
mine the glue spread from laboratory tests, dissolving 
a certain quantity of glue and determining the surface 
covered ?" My answer is, we may select the finest and 
most economical glue that money can buy, but unless 
the gluing department is right and the men apply and 
use glue correctly our spread test would avail us noth- 
ing. Your records should show what your glue costs 
are, and this is the real check on your gluing depart- 
ment. We will find some glue rooms equipped with the 
old style glue pots and the glue applied with a brush. 
We will find other modern rooms employing the latest 
types of glue-spreaders and find they cover a greater 
surface than the men daubbing the stock and likely 
wasting from ten to fifty per cent. If the surface of the 
stock covered is accounted for, the glue buyer will 
know that something is radically wrong. Yes, it is well 
to get a line on your spreading by testing, but in the 
name of common sense do not depend upon these tests. 

Suppose you buy a glue worth, say, thirty cents. It 
passes the required tests and is a pure hide product. 
The men in your glue room, however, abuse this prod- 
uct by overheating so that when actually used it is 
worth but twenty-five cents. What good was derived 
from your tests? Why not buy the twenty-five cent 
product in the first place and save the five cents that 
you are actually wasting? Therefore, our tests and the 


actual final result must be considered. When you know 
beyond the shadow of a doubt that your glue is prop- 
erly used and you are getting one hundred per cent 
glue room efficiency then you can apply the informa- PER CENT 
tion given regarding the spread of glue, but until this EFFICIENCY? 
degree of efficiency has been attained, your assumed 
spread cost is unreliable and cannot be depended upon. 



FIG. 19 


COMING to the practical end of the use of glue, we 
would say that in this day of rapid processes one 
must have a modern, up-to-date equipment in 
order to obtain best results. It is true that some very 
fine work was done in the olden times when the glue MODERN 
pot and brush, and the clamps or hand press comprised GLUE ROOM 
the entire glue room equipment, and the glue brush APPLIANCES 
and pot had to compete with the glue brush and pot; 
and the clamps and hand presses had to compete with 
the clamps and hand presses. But times have changed ; 
and one might as well expect the old stagecoach to com- 
pete today with the modern railroad flyer, or the old 
hand sickle to compete with a modern harvester, as to 
expect the old fashioned glue room equipment to com- 
pete with modern appliances. It is not merely a ques- 
tion of quality of work ; but in these times of keen com- 
petition time and cost are important items. Nor is this 
all. To do the amount of work demanded of the modern 
glue room in one of our large modern factories to do 
this amount of work with the old style equipment 
would require almost as much space as is now taken up 
by several departments; and in most factories floor 
space is an important matter. 

Glue room equipment has kept pace with the on- 
ward march of progress in other spheres of activity a 
steady march toward greater efficiency. All the 
changes that have been made in means of doing the 
work in the glue room have been for the purpose of 
making it easier to do the work in less time, and in- 
crease the quality where possible. The checking of 
veneer, owing to the presence of moisture before lay- 
ing, created a demand for the redryer; and the ten- 
dency of dry veneer to rapidly absorb moisture from 
the glue created a demand for something more rapid 
than the hand press, and the hydraulic press came into 
existence (Figure 19). The same may be said of the 



other modern machines. The retaining clamps and the 
overhead carriers came in response to a demand for 
economy in floor space, and to enable the one power 
press to do the work of many. The glue spreader (Fig- 
ure 20) responded to a hurry-up order froni the power 
press to keep it busy, as men could not spread glue fast 
enough with the brush. Then the modern glue dis- 
solver came to prevent these rapid machines from 

FIG. 20 


standing idle while glue was being prepared during 
the early part of the day. 

It is not enough that work be done well it must be 
done in the shortest possible time and in the easiest 
possible way ; and this can be done only by the use of 
the best equipment. Every manufacturer is anxious WORK MUST 
that the cost of operating his glue room be reduced to BE DONE IN 
the lowest possible point consistent with good work, THE SHORTEST 
and the result of our observation is a firm conviction POSSIBLE 
that the shops with the lowest operating expense are T 
those with the best equipment. The first cost of the 
plant is undoubtedly greater, but the difference be- 
tween a poor and a good equipment is soon wiped out 
by the saving in operating expense and the decrease in 
the cost of repairs. 

It is not our purpose to advocate any particular 
equipment, as every factory must be governed by its 
individual needs ; but we have been asked so often re- 
garding the best kind of caul for use in the veneer 
room that we might be permitted to say a word about 
this part of the equipment. There are three kinds of 
cauls in general use, i. e., wood, metal and fiber board. 
There are three kinds of metal cauls, i. e., iron, zinc and KINDS OF 
aluminum. It is not for us to advocate the claims of CAULS 
any of these, as many glue room operators have had 
success with all of them. But we will say that metal 
cauls should always be used where hot glue is the adhe- 
sive, because they will absorb and retain heat more 
readily than wood or fiber ; while we have a preference 
for fiber cauls where a cold glue is used, because they 
are light in weight and easy to handle. 

We have been frequently asked how best to prevent 
glue from sticking to cauls. In the case of fiber cauls 
they may be made glue-proof by repeated applications T o PREVENT 
of hot parafine oil into which parafine wax has been GLUE FROM 
melted in proportion of one pound of wax to a gallon of STICKING 
oil. Heat the oil as hot as can conveniently be done and T0 CAULS 
apply it until the caul will take in no more. The idea of 
the wax is to add body to the oil. A caul thus treated 
will last for a considerable time without anything 
further being done to it ; but to keep it in prime condi- 


tion it would be well to give it a light application of the 
oil at intervals, the length of which will depend on the 
frequency with which the caul is used. 

Metal cauls need something with a little more body 
than oil. Parafine wax has been used by some with fair 
success; but beeswax is better. For this purpose it is 
not necessary to use the genuine beeswax, as there is 
an artificial article that will answer the purpose 
equally well. 

With all cauls care should be taken to keep them 
clean ; and care should be taken in cleaning them. It is 
not a good plan to scrape cauls in cleaning, as this is 
liable to wear them thin in places, resulting in a 
reduced pressure at these thin points when in the 
press, which, in turn, results in blisters in the veneer. 
Metal cauls may be cleaned with steam or hot water, if 
one has a vat of hot water to put them in ; or they may 
be washed off with a rag and hot water. With fiber 
cauls there is less liability of the glue adhering to 
them, owing to their thorough saturation with oil, and 
if any does adhere it can easily be rubbed off. 

But cauls should always be examined for glue be- 

OAULS SHOULD fore being used, as any particles which may be present 

BE EXAMINED w ju k e pressed into the veneer, leaving dents which 

will likely rise and give no end of trouble during the 

process of finishing. 



TO GET best results in the use of glue, whether it 
be in gluing up solid lumber or in making 
veneered stock, one must have a proper place in 
which to do the work. A glue room located in a base- 
ment with a seven or eight foot ceiling is not conducive 
to the best in glued-up work; and this for more than 
one reason. Such a place is unfit for the work ; and a 
man capable of doing good work under proper condi- 
tions can easily find plenty of employment in more con- 
genial surroundings, and, therefore, is not likely to 
remain in such a place. 

An ideal glue room for doing veneer work is one 
located on the ground floor, because the light so neces- 
sary for matching fine veneers is better here than it is 
at a higher altitude; but for other purposes it is im- 
material whether it be located there or on the second 
floor. If located on the ground floor, and the floor is SHOULD SB 
cement with no basement beneath, it should be raised LOCATED ox 
to prevent dampness. GROUND 

The work of matching veneers and preparing the 
stock for gluing should not be done in the glue room 
proper; but should be done in a room immediately 
adjoining. In this room should be the machines for 
cutting the veneer to size and jointing and taping. Also 
immediately adjoining the glue room should be the 
drying room ; the nature and importance of which we 
will consider later on. 

The size of the glue room must, of course, depend 
on the volume of work to be done, but in laying it out 
it would be well to make provision for an expansion of 
business in order to avoid hampering the work through 

The success of a glue room depends a great deal on 
the arrangement of the equipment. If the work of glu- 
ing up the solid stock is done in the same room with the 







veneering, the appliances for doing the different work 
should be so separated that the work of one will not at 
any time interfere with the work of the other. As far 
as possible the revolving clamps and presses for the 
solid lumber work should be located at the side of the 
room to that where the veneering is done, leaving the 
space between the two equipments for stock in process. 

The glue heaters should be placed in one corner of 
the room with the glue spreader immediately in front 
of them. The heaters should be sufficiently elevated to 
allow the glue to flow into the upper and lower tanks 
of the spreader. This is preferable to carrying the glue 
from the heater to the spreader in buckets, which is 
liable to chill the glue and impair its quality. The glue 
should be run from the heater to the spreader through 
a detachable pipe ; and this should be taken down each 
night and cleaned along with the other utensils. 

The veneer laying bench should be placed in close 
proximity to the spreader and the power press as close 
to this as is practical, to avoid unnecessary carrying of 
the stock. Near the heater is a vat into which the uten- 
sils are put to soak to facilitate cleaning. This vat is 
provided with a drain-pipe and valve to allow empty- 
ing every day. 

The heating of the glue room is an important mat- 
ter. The forced hot-air system is not here recom- 
mended, as there is too much danger of the draft com- 
ing in direct contact with freshly glued surfaces and 
impairing the adhesive quality of the glue. The over- 
head steam coil is not recommended, because it heats 
the part of the room first that least requires it, and the 
part toward which the hot air will move in any event ; 
and in addition to this it is hard on the workmen. The 
most satisfactory system for heating will be found to 
consist of one or more coils of pipes placed along the 
walls about one foot from the floor, the number of 
pipes to the coil to be determined by the space to be 
heated, as well as the length of the coils. 

A well conceived glue room will have plenty of head 
room. Where animal glue is used, the odors are not of 
the most pleasant sort at the best of times, but are par- 



FIG. 21 








ticularly nauseating in a room with a ceiling so low 
that one feels as though he were in the midst of com- 
pressed offensiveness. No glue room should be less 
than eighteen feet high, and then a fan should be in- 
stalled for carrying off the foul air. This fan should be 
located near the ceiling at the opposite end of the room 
to the one where the spreader is in operation, and 
should revolve so as to draw the air out. This can be 
done without disturbing the air at any one point suf- 
ficiently to create a draft. Drawing air out with a fan 
is different from blowing air into a room by the same 
means. In the former case the air which is drawn out 
of the room is taken from the top and the air in all 
parts of the room moves upward to take the place of 
that which is being carried away. The movement of 
the air is so slow and even as to be imperceptible, there 
being no concentration except in the immediate vicin- 
ity of the fan. If the fan be reversed and the air blown 
into the room it will be forced toward a given point, 
creating a strong draft. 

The problem of how to admit fresh air to take the 
place of that drawn away by the fan may safely be left 
to solve itself. No room is airtight and the weight of 
the air outside will force fresh air in to take the place 
of that which escapes. 

The drying room to which we referred a short time 
ago should be considered an essential part of every 
glue room equipment. This room should be divided into 
two parts one part for warming stock before going in 
to be glued up, and the other part for drying stock 
after it has been glued up. The importance of warm- 
ing stock before gluing, and of drying thoroughly after 
gluing and before working up, are both considered in 
another part of this book. While we advise dividing 
this room into two compartments, we do not contend 
that it is absolutely necessary to do so. What we do 
claim is that the two rooms have an advantage over 
the one room. 

Where there are two rooms, one room can be used 
for warming the stock for gluing without running the 
risk of it being affected by the moisture that is being 


thrown off by the glued-up stock ; and into the second 
room the glued-up stock may be run to finish off a few 
hours before being worked up. 

Both of these rooms should be well heated and ven- 
tilated. If the room is large it would be well to place a 
coil of pipes in the center as well as along the wall, as 
this will increase and make more uniform the circula- 
tion of the air ; and circulation is essential to success in CIRCULATION 
a drying room. The heating apparatus should have a OJ , AIR 
sufficient radiation to keep the temperature in the ESSENTIAL 
vicinity of 110 degrees Fahrenheit. Ventilators should 
be placed in the top to allow the vaporized moisture to 
escape. In a several-story building, with the glue room 
and drying room on the ground floor, ventilators are 
not always practical; in which case a fan should be 
installed to carry off the moist air. 

The foregoing are the essential features of an ideal 
glue room connected with a wood working plant. But 
the IDEAL glue room would be a building one story 
high, with light from above as well as from all sides. 
Such a room would have to stand out by itself; and 
while it would be "ideal" from its own viewpoint, it 
would be inconvenient from the viewpoint of the other 
departments of the factory. 



AWAY back in the early dawn of the glue and 
woodworking industry men were trying, as 
they are today, to do the work in the best and 
easiest way. There is very little literature extant 
which would throw much light on the very early meth- 
ods of gluing up wood work, but the contrast between A BIT OF 
the methods employed half a century ago and those of HISTORY 
the present day is sufficiently great to be startling to 
the old-time cabinet maker, were he to leave his Celes- 
tial abode for a brief visit with us who were left behind 
to "carry on" after he had gone. In the early days the 
clamping-up was done by means of a frame not unlike 
the screw clamp in use today; but the pressure was 
exerted by means of wedges driven between the clamp 
and the edge of the boards to be pressed together. In 
those days the glue was dissolved in a kettle on a stove 
and brushes were the only means of applying it to the 
wood. A wonderful step forward was made when the 
screw clamp was brought into existence. There mat- 
ters rested for some considerable time; or until the 
trade of "cabinet maker" became divided into several 
different branches. In the old days the cabinet maker 
took the board in the rough from the yard and carried 
the work along, planing, jointing and gluing, assembl- 
ing and finishing until the article was completed. But 
when the furniture and kindred industries grew to be 
of national importance they outgrew the old fashioned 
method and the one trade of cabinet making became 
many trades; hence it is that we have the glue room 
specialist of today. With the advent of the glue room 
specialist this department became recognized as an 
important branch of the woodworking industry, and 
some of the best mechanical brains were directed to- 
ward improving the method of doing the work, so as 
to improve the quality and lessen the cost. 

Then the time came when the work of the glue room 





specialist was divided and some followed after the glu- 
ing-up of boards; and others followed the gluing of a 
face veneer on these boards. From this time on things 
moved with startling rapidity, so much so that a 
detailed account would read almost like a fairy tale. It 
is a long step from the old hand plane and glue brush 
to the modern automatic glue jointer, on which the 
lumber is jointed, glued, clamped and cut to size in one 
automatic operation ; and yet it is a step that has been 
taken by many men yet able to do a good day's work. 
It is equally far from the old glue kettle sitting on a 
stove to the modern steam or electrically heated dis- 
solver with its thermometer and automatic heat con- 
troller to prevent overheating and spoiling, and its 
power agitators to facilitate solution and reduce time 
and labor costs; and yet many who read this have 
spanned the distance. Measured from the viewpoint of 
accomplishment, it is a wonderful stride from the old 
glue brush and bucket to the modern glue spreader 
with its rolls designed to spread heavy or light, to 
spread on one side or both sides of the board, as the 
requirements of the work in hand may demand. The 
same may be said of the distance between the flatirons 
used in rubbing on veneers in ancient days and the 
clamps and clumsy hand presses of a later period: or 
between these and the quick-acting and powerful hy- 
draulic presses ; and from the old rack above the stove 
for drying veneers preparatory to gluing to the mod- 
ern redryer; and yet many who will read this have 
lived to see it all. 

All these things have tended to solve the problems 
of the glue room ; but there are many problems belong- 
ing to the individual glue room that yet remain to be 
solved. Equipment alone cannot solve them. The same 
high quality brain power that brought these machines 
into being must guide them in their operations if they 
are to accomplish all they were designed to do. At one 
time many were of the opinion that a machine was a 
failure if a man lacking in mental capacity could not 
keep it in successful operation. But the fact that a 
machine, no matter how perfected, is, after all, but a 



machine, without innert animation and but reflects the 
intelligence of its designer and builder in operating it, 
is now becoming more generally recognized. 

That the foregoing contention is correct is borne 
out by the experience of European countries, as well as 
by the experience and observation of those who have 
investigated the matter here at home. It will, we think, 
be pretty generally admitted that the average inhabi- 
tant of Europe does not give evidence of that high in- 
tellectual development that characterizes the average 
American. This lack of mental development is respon- WHY THE 
sible for the fact that in factories in Europe which are EUROPEAN 
equipped with American-made machines operated by LAGS IN 
men working for a much smaller wage than is paid in PRODUCTION 
this country, the cost of production is much higher 
there than here. These men, though steady and consci- 
entious in applying themselves to their tasks, do not 
seem to have the combination of head-heart-and-hands 
so essential to the speeding-up methods in vogue here. 
J. B. B. Stryker, who had traveled somewhat ex- 
tensively through Europe prior to the war and who 
visited numerous factories, in writing on the subject 
says : "Although American-made or modeled machin- 
ery is so largely employed by them, the production of 
the average plant, comparable with ours, as to size, 
equipment and number of men employed falls consider- 
ably short of the production over here." The same may 
be said of the factory in this country in which the 
average "foreign born" is placed in charge of machines 
so highly developed that all they seem to require is 
brain-power, but which deficiency the operator is 
unable to supply. 



FROM time as far back as the oldest glue room 
man's memory goes there has been more or less 
friction between the glue room and the finishing 
department ; and we do not think a book dealing with 
the problems of the glue room would be quite complete 
were it not to make some effort to set these depart- 
ments right in the eyes of each other. It is not our in- SHIFTING THE 
tention to take sides between these departments RESPONSIBILITY 
further than is merely incidental to the purpose of 
bringing order out of chaos. The great difficulty be- 
tween these departments has been and now is that 
when defects develop in the work, each department is 
more interested in trying to shift the responsibility 
from their own to other shoulders than in trying to 
ascertain the real truth regarding the actual cause of 
the trouble. And the fact that defects in wood work 
are not usually discovered until some time after the 
goods have arrived in the finishing department and the 
finishing process pretty well advanced, has tended to 
intensify the difficulty by giving the glue room some 
ground for the assertion that the goods were all right 
when they went into the finishing room, and that some 
material used in the process of finishing must be re- 
sponsible for the trouble. 

The finishing department, on the other hand, when 
defects develop, is equally positive that the method of 
finishing is not in any way injurious to the glue or in 
any way responsible for the defects ; and declares that 
the defects were hidden in the woodwork before being 
sent to be finished; and that had the glue men done 
their work right no trouble would have ensued. And 
thus the argument proceeds ad infinitum. 

Take, for instance, the matter of blisters in VENEER 
veneered work. As a rule, these do not show them- BLISTERS 
selves until the goods have received at least a coat of 







stain perhaps of water stain. Or the finisher may 
have sponged the stock with water to raise the grain, 
all of which furnishes the glue man with a lever with 
which to roll from his own door to that of the finishing 
department the responsibility for the trouble. But let 
us look at the matter calmly for a moment. Let us take 
a piece of veneered work about the soundness of which 
there can be no doubt, and let us try and remove the 
face veneer by soaking it with water, using a brush or 
sponge to apply the water. We put on one coat, two 
coats, three coats, six coats, and still the veneer sticks 
tight. Now if half a dozen applications of water will 
not loosen veneer when we want to remove it, is it 
reasonable to say that one coat of water stain or a light 
sponging with water caused the blisters in the finish- 
ing room ? Let us be honest with ourselves, even if we 
don't want to be with the other fellow. We will be 
much wiser in the end if we are. 

If veneer is well and truly laid, neither sponging 
nor one or two coats of water stain will loosen it. And 
if it be not well laid, or if there be any doubt about it, 
the best thing that one can do is to go over it with a 
sponge and water and by this test ascertain the facts. 
A usual test for blisters is to lightly tap the veneer 
with the finger, and if the response is a sharp "click" 
we know the veneer is loose. But this test is not always 
reliable, because the veneer may not be cemented to the 
core and yet be lying sufficiently close to prevent the 
telltale click when tapped with the finger ; and yet the 
very moment it is touched with water it will raise in a 
blister. Now why is this so ? Let us explain : 

The normal state for the veneer would be lying close 
to the core ; it was that way when it left the press, and 
there has been nothing done since to change this condi- 
tion. But when we touch the veneer with water we 
change the normal condition by causing the fibers to 
swell and the veneer to tighten and become too large 
for the place it is in, and it raises up to relieve the 
strain. But it can raise only if it is already loose from 
the core, because if it is firmly cemented to the core the 
strain thus imposed could not possibly be sufficient to 


break the glue joint. The same thing may be illus- 
trated in another way: take a sheet of paper, spread 
it out on the table, and draw a wet sponge part way 
across the center, and see how quickly it wrinkles up. 
The moist piece at once becomes too large for the place 
it occupies and expands in several directions. But the 
paper would not have wrinkled had it been firmly 
cemented to a heavy body, which fact can easily be 
demonstrated by the simple test of trying to remove 
wall paper by the same process. 

We recall the case of a concern which had more 
than its share of trouble with loose veneer and open 
joints, without being able to ascertain the cause TROUBLE IN 
for some time. The glue room men and the ONE FACTORY 
cabinet room foreman, under whose supervision the 
glue room work was done, all contended that the cause 
of the trouble lay hidden in the dark recess of a large 
oil-stain vat into which the stock was dipped on reach- 
ing the finishing room. Things were finally brought to 
a head by the finisher being ordered to discontinue the 
use of the vat; but he demanded some proof that the 
vat was the cause of the trouble. No proof being forth- 
coming, the finisher proposed to prove that the vat was 
not guilty as charged, and offered to submit it to any 
test that might be suggested. To this end a cake of glue 
and two or three panels which gave evidence of being 
sound were put in the vat and left there for twenty- 
four hours. Then, at the end of that time, the glue and 
panels were removed, without showing any evidence of 
ill effects from their long immersion, the management 
decided that they must look elsewhere for the hidden 
mystery, and turned their attention to the glue room. 
When this was done they were not long in finding what 
they were after, in the shape of over-cooked glue and 
over-heated cauls. Having made this discovery, their 
troubles from this source were at an end. 

Men are not unlike mere material matter, in that 
they are prone to follow the course of least resistance, 
and in the case under consideration, when defects are 
found in glued-up work it is much easier to look for the 
cause in the immediate vicinity of the place where the 






defects are first discovered and find some operation, 
the nature of which we do not understand, on which to 
lay the blame, than to make a diligent search where we 
are likely to find out what we are after. To be quite 
frank about it, it too frequently happens that neither 
the glue man nor the finisher is quite positive that the 
cause of the trouble is not in his own department, and 
for this reason is not very anxious to find what he 
is hunting for. 

It is a mistake for a man to remain in ignorance of 
even small matters merely because he lacks the moral 
courage to face the truth. There is no man so perfect 
that he never makes mistaks. Some one has said that 
"the man who never made a mistake never made any- 
thing that was worth while." And it is not the man 
who runs away from his mistakes or tries to hide them 
that succeeds the best in life. On the contrary, the man 
who succeeds is he who acknowledges his mistakes, 
grapples with them and overthrows them and uses 
them as stepping stones to great achievements. 

Let the finisher and the glue room man determine 
in his own heart that he will be honest with himself 
and honest with the other fellow. Let these two men 
come together with that thought uppermost in their 
minds when defects appear in glued-up stock ; let them 
together search for the cause with a determination to 
find it, no matter where it is to be found, and each will 
find that he has dropped many a headache, and many a 
heartache as well. 



ONE of the most difficult things which the man 
who lays veneer finds himself up against at 
times is the problem of getting a good, tight glue 
joint on the scroll and other irregular work. To over- 
come this difficulty, various schemes have been tried in 
various places, with equally varying results. The most 
common practice is that of applying extra pressure in 
the hope that in some way the low spot where the 
veneer is liable to be loose will be reached and suffici- 
ent pressure applied to produce the desired result. 

There is one thing which it would be well for all of 
us to remember, and that is that everything has a 
cause, and that a repetition of the difficulty before us 
may be avoided by removing the cause. When we re- 
move the cause, the effect must cease. The whole thing FIND THE 
may be summed up in the maxim that "An ounce of CAUSE 
prevention is better than a pound of cure." In the 
case before us, instead of applying a sufficient amount 
of extra pressure to crush the article out of shape, as 
I have often known to be done, it would be better to 
start at the point of the trouble and trace back until 
we find the cause, or the reason why the pressure is 
not uniform all over. Having found it, let us remove 
it, no matter what it may be. 

Not infrequently the cause of the difficulty is in the 
design of the article to be veneered. It all too fre- 
quently happens that the designer is not a practical 
mechanic, in consequence of which the veneer man is 
often asked to do the impossible. Many times a slight 
change which would not materially affect the appear- DESIGNS 
ance of the article, nor alter the designer's conception, MUS f BE 
would eliminate mechanical difficulties and greatly les- PRACTICAL 
sen the manufacturing cost. Many designers submit 
their drawings to a practical man and make the sug- 
gested alterations. But there are a few who know so 
little about the things of which they are supposed to 





know considerable that they feel they must guard that 
little with jealous care hence they resent any sugges- 
tions regarding the offspring of their brain. When I 
find one of these men I cannot help making him an ob- 
ject of mingled pity and contempt. Pity because he is 
small, and will never be any bigger. The designer who 
is worthy the name has nothing to fear. He is a big 
man in the profession. He has had his eyes open to see 
and his ears open to hear anything that might be sug- 
gested to him. But the small man he is small because 
he refused to open his mind to imbibe that which would 
have made him big. Under the most favorable condi- 
tions it is not an easy matter to get a first-class, de- 
pendable glue joint on scroll work; hence the impor- 
tance of eliminating everything that would make it 
more difficult. 

But even where every care has been taken by the 
designer to remove all unnecessary difficulties, it is not 
always possible for the veneer layer to produce the de- 
sired result, although through no fault of his own, and 
in consequence of something over which he has no con- 
trol. It is the common practice, and rightly so, to use 
as a caul the piece bandsawed from the scroll. Now, in 
order to make ourselves quite clear, let us discuss the 
matter before us as though we were presenting it to a 
class of boys in school. Let us take the scroll to be 
veneered and lay it on its side on the bench ; then take 
the piece which was cut away, and which we are to use 
as a caul ,and lay it beside the scroll, being careful to 
have the two pieces separated by the thickness of the 
saw which was used to cut the two apart. Having done 
this, we will look along the various curves and lines 
and we will observe that at all points the distance be- 
tween the two pieces is exactly the same. If we move 
them a little closer together we will .observe that at 
certain points they are nearer each other than at other 
points. The same thing will be seen if we move them 
farther apart instead of closer together. If we move 
the two pieces together until they meet we will see that 
they touch at certain points only. Now, in what we 
have just pointed out is to be found the reason why it 



is so difficult to get a good, tight glue joint between the 
veneer and the surface of the scroll on which it is laid ; 
and in the same thing is to be found a solution of the 
problem which the subject presents. To illustrate : 

Suppose we bandsaw a scroll, using a saw set to 
make a cut 1/20-in. in width. Having done this, we 
place the scroll and the caul on the bench separated by 
exactly 1/20-in. at any one point and we will see that 
they are an equal distance apart at all points. Now 
take a piece of veneer 1/20-in. in thickness and slip it 
in between the caul and the scroll, and you will find 
that the fit is perfect at all points. 

Now, suppose we remove the 1/20-in. veneer and 
substitute a piece 1/30-in. in thickness, and press the 
caul and scroll together to fill in the space resulting 
from the difference in the thickness of the two veneers 
and we will find that at certain points the veneer is 
tight, while at other points it is quite slack. 

Now, let us remove the 1/30-in. piece of veneer and 
fill the space with a piece 1/16-in. thick and we will find 
the conditions the very reverse of what they were 
before; the points which were tight with the 1/30-in. 
veneer are now slack ; and where it was formerly slack 
it is now tight. 

All this goes to show that the problem of a tight 
glue joint on scroll work is in the use of a veneer ex- 
actly the same thickness as the kerf removed by the 
saw. Of course, there are other things of importance 
to be attended to. Good judgment must be exercised in 
applying the pressure. Where the pressure must be 
applied from two directions it should be applied to the 
smaller surface first, otherwise it may be found diffi- 
cult, if not in some instances impossible, to overcome 
the resistance offered by the greater pressure on the 
larger surface to insure a tight joint at these smaller 




THE first requisite to the successful laying of face 
veneer for fine cabinet work is the quality of the 
veneer itself. We may have a good core well 
crossbanded ; and we may employ the most skilled help 
to do the work with the best of glue ; but if the veneer 
is of a poor quality our work will count for naught. It 
is not enough that veneer be well figured to be classed 
as good stock ; it must be well cut, and well cared for, 
and well dried otherwise we are merely building 
trouble for the future into our work. 

A great deal of our best figured veneer has the 
fiber so badly ruptured as to make it extremely diffi- 
cult, if not quite impossible, to lay it with any degree of 
assurance that trouble will not develop; and for this 
reason one should exercise the utmost care in selecting 
the stock for fine face work. The more beautiful the 
figure of the wood, the more difficult it is to cut into GOOD 
veneer without doing damage to the fibers. The figure K 
is the result of the entwining and interlacing of the 
wood fibers in such a way that when cut into veneer 
many of the fibers are cut into lengths no longer than 
the thickness of the veneer, which may be as fine as 
1/30-in., and sometimes even less. These short fibers, 
which run straight, or almost so from one side of the 
veneer to the other, make what is called "end wood ;" 
and unless the veneer is handled very carefully it is 
very liable to check at these places. It also makes it 
very difficult to dry without checking, as the difference 
in the grain is such that some parts dry out faster than 
others; and this uneven drying means uneven shrink- 
ing, and this sets up strains in the wood which certain 
parts are unable to withstand; and they break. For 
this reason, veneer, when once dry, should be kept dry, 
in order to reduce to a minimum the possibility of 

But too much care cannot be exercised to insure the 







veneer being dry before laying. It would be safe to say 
that nine-tenths of the trouble with veneered work re- 
sults from the veneer not being dry at the time of lay- 
ing ; or, more properly speaking, at the time the press- 
ure is applied. We may have the veneer thoroughly dry 
at the time of laying on the core, and by leaving it loose 
so that it absorbs moisture from the glue and swells 
before the pressure is applied we may defeat all our 
efforts in drying. 

Where one has considerable veneering to do it will 
pay to put in a redryer. It is not our intention to advo- 
cate the claims of any one make, as all have merits 
worth considering; and the buyer must be guided by 
the work in hand and select the machine best adapted 
to meet his own peculiar requirements. But if one is 
starting in a small way, or, for instance, in a manual 
training school, it would not be the part of wisdom to 
go to the expense of installing an expensive redryer. 
Under such circumstances one must adopt other means 
to accomplish the desired result. Take boards of some 
soft, absorbing wood, such as basswood, and cut them 
in size a little larger than the veneer to be redryed. 
Heat these boards as hot as possible in the hot-box and 
lay the sheets of veneer between the boards, keeping 
each sheet separate, and put under pressure, applying 
a heavy pressure for a few moments at the start to 
allow the veneer to heat quickly ; then loosen the press- 
ure to allow the veneer to shrink, as the boards absorb 
the moisture, without the danger of checking. 

Much of the finest face veneer, such as crotch and 
burl walnut, is badly buckled when dry, and cannot be 
laid in this condition without breaking when the press- 
ure is applied. Stock of this kind may be moistened 
with water sufficiently to allow it to be flattened out 
with safety, then redried in the manner described 

For the benefit of any who may not know what the 
hot-box is spoken of above it might be well to describe 
the form of construction. There are many different 
ways of making hot-boxes ; some being made of boards, 
but the principle is the same in each case and we will 


describe the box which we think to be the best. It is a 
metal box made from sheet iron. If a large box is re- 
quired it is made in sections fastened together with 
angle-irons. The sheet-iron is made into panels, two SH EET 
sheets to a panel with sheet asbestos in the center. Into IRON 
this box steam pipe coils are placed in such a way that HOT BOX 
they may be used as shelves ; the number of shelves and 
the distance apart depending on the size of the box 
and the work to be done. This box is different from a 
drying room; the idea here being to get a maximum 
heat in a minimum time. For heating, either exhaust 
or live steam may be used. If a trap is placed at the 
outlet of the coils it will cost very little to heat with 
live steam. The stock to be heated is placed on the 
coils of pipe. There should be a vent at the top of the 
box to allow any moisture that may be present to 
escape ; as the boards to be heated must be absolutely 
devoid of moisture to do the best work. 

With the stock thoroughly dry it is ready to be 
jointed and taped if it is narrow stock. Whether ore 
has a taping machine in his factory should depend on 
the amount of work he has to do ; but one man with a 
taping machine can tape as much stock as half a dozen 
men can by hand; and as the machines are compara- 
tively inexpensive, it would be well to give the matter 
very serious consideration before deciding that you can 
afford to do without one. 

The usual method of taping veneer is to tack one 
piece to a board, using very fine brads for the purpose, TAPING 
so as not to make too large a hole, then fitting the edge VENEER 
of the second piece close to the edge of the first piece, 
being careful to match the grain and figure, and tack- 
ing it down in like manner. But this method has disad- 
vantages as it takes time to tack the veneer to the 
board as well as time to remove it after the taping has 
been done. The tack holes must also be considered, for, 
no matter how careful one may be, and no matter how 
small a brad he may use, in some veneer the mark will 

A better way to tape by hand, but one which re- 



First operation: Moisten tape and run it along edge of veneer, 
allowing one-half to project over for the next piece 

Veneer reversed with gummed side of tape up ready to 
receive its mate 

The two pieces joined ready for laying 
FIG. 22 


quires some skill, especially with long joints, is to place 
the sheet of veneer on the taping bench with the side to 
be taped upward (Figure 22.) Moisten the tape and 
run it along the edge of the veneer; one-half on the 
veneer and the other half projecting over. Then turn 
the veneer over. This brings the gummed side of the 
tape upward ready to receive the second piece of 
veneer. Speed and skill are necessary to get both 
j)ieces in position while the tape is sufficiently moist 
to take a good hold ; but with a little practice one can 
become most proficient. 

Never spread the glue on the veneer, as to do so will SPREAD THE 
destroy all the good effects of redrying. After the GLUE ON 
glue has been spread on the core it should be allowed to THE CORE 
set for a few minutes to become slightly "tacky." This 
will allow some of the moisture to penetrate the core 
where it will be comparatively harmless; otherwise 
much of it will enter the veneer before it can be gotten 
under pressure. And let us say to get the stock under 
pressure at the earliest possible moment after the 
veneer touches the glue in order to prevent the veneer 
swelling through the absorption of moisture from the 

And in this connection let us not confuse cause and 
effect. In removing moisture from veneer by the pro 
cess known as redrying we have two objects in view. 
It is very seldom that veneer which has once been dried 
contains a sufficient amount of moisture to prove a 
detriment to the glue; hence the removal of the mois- 
ture is of secondary consideration. Moisture in veneer 
is a cause and not an effect. It is the cause of expan- 
sion in the veneer ; and it is to decrease this expansion 
that we remove the moisture. If the veneer is laid in to 
this expanded condition and becomes firmly cemented 
to the core it cannot shrink back to its normal width 
during the process of drying the built-up stock that 
is, it cannot draw in from the edges. The fibers them- 
selves will shrink, and will separate one from the 
other, making very fine checks in some instances; and 
in others larger ones. It is to prevent this that we re- 
move the moisture before laying the veneer when it 







can shrink to a minimum width without injury to the 

To prevent the veneer expanding through absorb- 
ing moisture from the glue we advise getting the stock 
under pressure as soon as possible after glue and 
veneer come together. There are many who have the 
idea that so long as the veneer was made thoroughly 
dry before being laid all danger along this line has 
passed; but a more fallacious idea could scarcely be 
entertained. It is at this point that the real danger 
exists. It is seldom that a veneer which has once been 
dried will contain as large a percentage of moisture 
before being laid as will be found in a redried veneer 
two minutes after it has come in contact with the glue. 
One should not lose sight of the fact: It makes no 
difference how, when or where the veneer gets the 
moisture that expands it whether the dews of heaven 
descend upon it; whether it gets it from the atmos- 
phere during a period of high humidity or gets it from 
the glue just prior to going under pressure, the effect 
is the same expansion. And it makes no difference 
how, when or where this expansion was brought about, 
the effect is the same contraction ; and the inevitable 
result of the shrinking veneer after it is laid is : checks. 

Not a few people have trouble with butt joints 
opening after the veneer is laid. These openings are 
not always uniform ; and they do not always extend the 
full length of the joint. This has frequently given rise 
to the suggestion that the man who jointed and taped 
the stock was careless about his work; and has fre- 
quently resulted in much confusion and no little ill feel- 
ing. But no matter how well stock may be jointed and 
raped it will open in certain places if allowed to absorb 
moisture from the glue before it receives the pressure. 

Wood does not expand uniformly at all points. In 
the case of crotch veneer the difference in fiber and 
texture of the different figures allows great scope for 
this uneven swelling; and when those places along the 
edge of the joint which expand more rapidly than 
others, do so, and press against each other they sepa- 


rate the slower swelling parts hence the uneven, open 

The remedy for this is the same as for checks, i. e., 
get the pressure on before the veneer can swell, for 
under heavy pressure it cannot move. THE LESSER 

In laying crotch veneer on ogee drawer fronts and OF TWO 
other shaped work some have resorted to moistening EVILS 
the veneer with water to prevent breaking. This is all 
right as far as it goes ; but it does not go far enough. 
Those who follow this practice admit they have plenty 
of trouble with the veneer checking; but they claim 
the checks are not as bad as would result from laying 
the veneer when dry ; and of two evils they are choos- 
ing the least. 

But there is no necessity for making a choice be- 
tween these two evils ; for both may easily be avoided. 
Make some forms duplicates of the forms to be ve- 
neered ; using basswood, or some other absorbing wood 
for the purpose; and heat them in the hot-box. 
Moisten the veneer with water to render it pliable ; and 
when sufficiently so bend it to shape in the duplicate 
forms under pressure the same as when laying the ve- 
neer permanently. The usual amount of moisture in 
veneer thus treated will make it difficult for one form 
to insure its complete elimination. For this reason it 
would be well to either re-heat the forms and make a 
second application, or place the veneer in the drying 
room for a short time. It will retain its form, so that 
no trouble need be anticipated from that direction. 

Where animal glue is used for veneer it is necessary 
to use warm (not hot) cauls, which help to keep the ugE 
glue in a liquid state for a longer period of time than WARM 
would otherwise be the case, enabling it to more firmly CAU LS 
unite with the wood. Let us lay emphasis on the im- 
portance of the cauls being at the right temperature. 
The heat in the caul helps to diffuse the moisture in the 
glue ; driving it into the core ; and the hotter the caul 
the more rapidly it drives it away. This is as it should 
be, for in the core the moisture can do no harm. But if 
the caul is not hot this rapid diffusion of the moisture 
creates a source of danger, as it leaves the glue in a 


dry state devoid of the protection of the moisture, in 
which condition it is very easily injured by heat. This 
CAULS SHOULD can be better understood when we remember that the 
NOT BE h ea t required to prepare the glue for use would render 

it absolutely useless were it not for the protection 
furnished by the water which it contains. Cauls 
should never be made so hot that they cannot be read- 
ily handled with the bare hands, in which condition 
they can do no harm. 



ONE cannot do good work with inferior glue, but 
he can do very poor work with the best glue if 
he does not use it right. The glue-mixer may 
have his solution in the best possible condition, but all 
his care will be far nought unless those who use it 
afterward understand what is required of them. "The 
chain is no stronger than its weakest link" is a maxim 
no more true anywhere than here. All through the 
process of building glued-up stock every detail requires 
intelligent and careful attention, otherwise there will 
be a weak link in the chain of operations because of 
some neglected detail and the work will fall down at 
that particular point. 

The spread of glue must be uniform and of the cor- 
rect weight. For this reason glue-spreading machines 
are preferable to the old-time brush and glue pot, as 
the spread is evenly placed all over each piece and each GLUE SPRE AD 
piece is spread alike. But the operator of the mechani- MUST BE 
cal glue-spreader must understand the weight of EVEN 
spread required for the work in hand, otherwise the 
spread may be too heavy or too light and defective 
work will result. 

Much poor work results from a too heavy applica- 
tion of a heavy glue solution. It is obvious that an in- 
sufficient quantity of glue to the joint will result in 
defects sooner or later ; but not every one can see that 
an over-application of glue is equally bad. If one puts 
on an excessive amount of glue of a heavy consistency 
and allows it to stand until it becomes tacky there is 
danger of the surplus not squeezing out, and thus leav- 
ing an excessive amount in the joint. Where this 
occurs, the glue, in shrinking during the process of 
drying, is much more liable to break away from the 
veneer, allowing the latter to raise in places in the 
form of blisters. 

The modern mechanical glue-spreader has one seri- 





ous defect it has no brains; but I am sometimes 
inclined to think that it has about as much of tnat com- 
modity as many men who are allowed to spread glue 
with a brush in some shops. Some employers appear 
to have the idea that the mechanical glue-spreader has 
brains of its own, and that a further supply is unneces- 
sary, and they put a man in charge of the machine who 
gives no evidence of being in possession of that prime 

From almost every viewpoint the mechanical glue- 
spreader is essential to the success of the veneering 
department ; and especially is it an economic necessity. 
It will do more and better work than can be done at 
the same cost when done by hand; and it conserves 
glue, which is no inconsiderable item at the present 
time with the prevailing high prices. More glue than is 
necessary is not put on the stock ; and the glue is not 
wasted by splashing everything around. In many 
plants the saving of glue through the prevention of 
waste alone would soon pay for the machine. 

In operating the mechanical glue-spreader one 
must give special attention to the speed, for if run too 
fast it will unduly agitate the glue and cause it to foam. 
If the glue should foam, suspend operations at once 
until the cause of the foaming has been ascertained. 
Some glue will foam much more readily than others 
for which there may be various causes. If the foaming 
continues under a reduced speed the cause will be in 
the glue ; the thing then to do is to examine local con- 
ditions to ascertain if the cause of the trouble is in the 
shop or came with the glue. 

If the glue is fresh and the dissolver was clean be- 
fore the glue was mixed, and the spreader was thor- 
oughly cleaned before it received the solution and the 
glue has not been overheated, then it is pretty safe to 
conclude that the cause is not local ; but is inherent in 
the glue. 

Some experiments have shown that glue foaming 
may be caused by the entire absence of grease from 
the glue. Good glue intended for brush work usually 
contains no grease, this having all been extracted dur- 


ing the process of making. When such glue is intended 
for the spreader, and the manufacturer knows the pur- 
pose for which it is intended he will usually add a suffi- 
cient quantity of cocoanut oil to prevent foaming. A 
serious case of foaming has been checked by adding a 
piece of beef tallow the size of a marble to each gallon 
of the glue solution. This amount, though sufficient to 
prevent foaming, would have no appreciable effect on 
the adhesive quality of the glue. 

There are other causes of foaming, but all point to GOOD WORK 
inferiority in quality. Cheap bone glues are prone to REQUIRES 
foam when used in the spreader; and glue that has GOOD QLUE 
been over-limed will do likewise. Such glues should 
not be used where good work is expected to result. 



SALESMANSHIP has been advanced to a science. 
It is no longer a wierd and mysterious magic by 
which one man influences another to buy from 
him an article which he may or may not want. It is no 
longer, as it was in the early ages, an exchange of 
necessary commodities. It is no longer a happy hunt- 
ing ground for the shrewd and unscrupulous, but it has THE SCIENCE 
evolved from its first stages of necessary exchange, OF SALES- 
through all the mazes of charlatanry, bringing with it MANSHIP 
the best from each stage, until it has grown into a sci- 
ence and profession. Slower than the professions of 
the physician and chemist in its development, it has, 
however, reached a degree now, in which it is building 
Its own etiquette and coming to its own recognition. 

In view of this modern science of salesmanship, I 
shall attempt to give my ideas of the scientific selling 
of glues. 

It is very true that there are certain lines of busi- 
ness in which the salesman has no competition; this, 
however, is the exception. There are many lines in 
which the competition is more imaginary than real; 
that is to say, the quality of the goods of the so-called 
competitor is so much inferior to that of the goods car- 
ried by a first-rate manufacturer that there is no reaJ 
competition. The buyer, however, who is usually 
shrewd, and, unfortunately is often unscrupulous, will, 
if possible, lead the salesman to think that competitors 
have given better prices or better terms, and that their 
goods are superior. The salesman who is not armed at 
every point to meet his tactics runs the risk of being 
imposed upon. 

We know absolutely that most manufacturers, job- THE CUSTOMER 
bers and dealers of glues desire to please the customer MUST BE 
and will endeavor in every way to hold up the grade PLEASED 
that is being bought. These men know absolutely that 
many buyers will try to buy glues at low prices and 








some buyers may "bluff" the salesman. In most cases 
it has been due to the salesman's ignorance that the 
sale was lost. Again, nothing will destroy a buyer's 
confidence more quickly than to find a salesman ignor- 
ant of the claims made by his own house, or of the spe- 
cific qualities of the glues offered for sale. All sales- 
men need to keep themselves fresh and enthusiastic in 
regard to their goods, not only by frequently visiting 
their factories, keeping in touch with the qualities of 
all boilings, but also by reading all literature applica- 
ble to glue and glue testing. Therefore, do not super- 
ficially peruse the pages of this valuable book. Read all 
the material contained herein time and again and the 
writer knows absolutely that if the information is ap- 
plied, the salesman's success is assured. 

Get all the information you can from the salesmen 
of competing factories. Learn all you can in an open 
fair way, but do not resort to trickery, or to any meth- 
ods which you would be unwilling to have a competitor 
use with your house. Do not attempt to sell goods until 
you know absolutely that you can meet any argument 
and that your line of talk is of such character that 
there will be no doubt in the mind of the buyer that you 
are not a novice, not a traveling man trying to put 
something over, but a real glue salesman in all that the 
name implies. 

It is to be regretted that there actually are glue 
salesmen who seem to delight in "knocking their com- 
petitors." I have met men who deliberately knocked 
high grade glues, comparing them in quality with low 
grade products. A certain salesman sold hundreds of 
tons of grade 1^4 glue for joint purposes and claimed 
his glue would compare wih any joint glue regardless 
of price. His argument was that his glue did rot take 
as much water as most hide glues, but it is of the high- 
est quality as a joint product. Very fortunately the 
writer made joint determinations in the presence of 
the salesman and his glue was used in the test. This 
man has not called at my office since and he did finally 
say: "It takes a salesman to get by with my line of 
'stuff,' but the man selling high grade glues at a reas- 


enable or low price is not a salesman but an order 

So many salesmen seem to suppose that business is 
done largely on friendship. "Friendship and business 
don't mix," is an old adage and a true one. You can't 
presume on your intimacy with a man to sell him 
goods; and it is seldom you can get his trade away 
from a successful salesman, even if you have identical 
grades and quote the same prices. There is no doubt 
that business friendship plays a very large part in 
business getting with all salesmen. You know how 
hard it often is to break in on the trade of another 
man, simply because he has won the friendship of his DON'T PRESUME 
customers. Keep this in mind, but please remember TOO MUCH ON 
that if your goods are right and the price reasonable, FRIENDSHIP 
you have nothing to fear, especially so if you merit the 
confidence of your trade. I have known of buyers pur- 
chasing glues from one factory for more than thirty 
years. They finally came to their senses though and 
now every reputable glue house known to them gets a 
chance at their business. 

To be a successful glue salesman it is absolutely es- 
sential to become familiar with practically all the dif- 
ferent lines employing glues or other adhesives in their 
work. For instance, in selling glues to manufacturers 
of wall paper it is necessary to offer only such glues as 
are free from foam. The glue must also be free from 
mucin and soaps which will not affiliate with the colors 
or clay. He will not offer glues to textile manufactur- 
ers containing mineral acids and normal sulphites 
since any notable proportions of these impurities will 
reproduce light patches on dyed wool. He is also very 
careful in offering glues free from coloring agents that 
will injure the shades of silks. He knows that pale 
glues have been bleached with sulphuric acid, traces, 
and frequently more than traces of which remain in 
the glue, as well as salts of sulphurous acid. When sell- 
ing to manufacturers of paper boxes, the salesman 
appreciates that either animal .or the vegetable glues 
may be used to good advantage. He knows that where 
gloss or the finish of a good covering paper has to be 





preserved, the animal glue has preference. When 
asked why he will say, because the pastes, and some 
gums have so much water in them that the gloss is im- 
paired. He also knows that the drawbacks of animal 
glues are higher prices and that in this respect the 
vegetable glues have the advantage. Mr. Glue Sales- 
man does not lose sight of the fact that various box 
factories offer different problems and every problem 
deserves study and well "thought out" solutions. In- 
deed, there is hardly an article manufactured in the 
making of which glue does not play a very important 
part in some form or other. 

The salesman should, if possible, be practical. Some 
of the things that the salesman can do along this line 
are trivial. Some, on the other hand, are big. The 
representative who can give the men in the glue room 
valuable tips, is always welcome and the superinten- 
dent or foreman may ask the purchaser of glues from 
time to time, "When is So and So coming? That fellow 
understands his business and I would like to have him 
assist me in solving a very perplexing glue problem." 
Truly, the salesman who can do these things is tying 
his customers to him with ropes of steel and will make 
his visits an event instead of a call. 

When visiting a propect endeavor in every way 
to obtain samples of the glues he is using and mail 
these promptly to your factory laboratories for analy- 
sis. The factory manager should insist upon having 
samples tested on the same day they arrive, or as soon 
thereafter as possible. In the event of a big contract 
being at stake and there being a likelihood of the con- 
tract being signed within a very few days, the sales- 
man should do the testing at the prospective place of 
business. Should this be impossible, make a few im- 
portant tests at the hotel. I would suggest the carry- 
ing of a viscosimeter, balance, litmus papers and a few 
beakers. The jelly can in such extreme cases be tested 
by what is known as the "finger test" fully explained in 
other pages of this book. A suitable thermometer can 
be carried in the vest pocket, in fact, it is as necessary 
for a good glue salesman to carry such an instrument 


as it is for the physician. Stick (as you would have 
your glue do) until you have closed the deal. Remem- 
ber, you are in a sticky line so never say "quit." 

If you want to reach the high mark in the selling of 
glue, you have to have overwhelming belief in yourself 
and not only in the glues you sell, but in the house that 
manufactures them, and you must believe in yourself 
first of all. Extravagant hope and confidence are 
necessary. This is one place where extravagance is an 

Enthusiasm is the great, far-reaching wisdom of 
faith it prompts and sustains the noblest efforts. If 
you have it you should be thankful and if you have the 
brand that is contagious, you are a public benefactor 
and a record-breaker so far as sales go. Never, Never, 
NEVER ! show a weakness in your argument or gen- 
eral sales talk, for this will be detected and like E 
enthusiasm, is contagious. Do not because a man buys 
tons of glue every year, be afraid of him and feel more 
at home in the small hardware store selling probably 
twenty-five pounds annually. Your prospects must 
never be approached with timidity, an "excuse-me-for- 
living" attitude. You are or should be just as good a 
man as the purchasing agent. 

One grave mistake I find so many salesman make, 
especially men representing very large glue factories, 
is to "jump towns" and call up over long distance tele- 
phone from some neighboring city and say in a seem- 
ingly bored way : "Went through your town this after- 
noon, but really it does not pay me to stop off in small 
cities, for you know I'm representing a very large glue 01 
house and we must keep moving. Anything doing in 
the glue line today?" Such men are not salesmen, but 
may be classed as mere order takers. Of course, it 
may at times be necessary to resort to the telephone, 
but do not do so unless it is absolutely necessary and 
you are very well acquainted with the purchaser, 
knowing that he will not be offended. 

Don't ignore questions about competitors, and don't 
fail to banish from the customer's mind all doubts and 
prejudices, but it is a serious mistake to spend a lot of 





time talking about competitors' glues when you ought 
to be sticking to the merits of your own. Answer 
quickly all questions, and then switch back to the excel- 
lence of your product. Be so enthusiastic about your 
own selling points that rivalry will be forgotten. In 
meeting competition, do not be fooled by the question 
of price. At present, very many lines are of practically 
the same quality, grades considered, and prices are 
about the same, so that you must bring out, as a high 
grade salesman should, the fact that service is the 
main consideration. Show what your house can do in 
the matter of prompt deliveries, careful packing of 
glues, dependability as regards uniform quality, 
correct weight, liberal terms, etc., and do not forget 
that the general reputation of your house is a selling 
point. The facilities which you have for keeping 
abreast with the times, like the employing of expert 
chemists and engineers in your laboratories to do your 
experimental and research work, thereby improving 
the quality of your glues all the time, is a point of serv- 
ice well worth consideration. 

Above all, a glue salesman can meet competition 
most effectively by a strong personality. Remember 
that your glues are judged by yourself, sometimes 
even unfairly; and remember that we are always 
judged by our weakest points; hence, in order to hold 
your trade from competitors, and to get new trade, 
you must possess what is commonly called "business 
magnetism," which is another way of saying a strong 

A salesman called at my office a few years ago clad 
in a "Prince Albert" coat, very delicate kid gloves, a 
silk hat, highly polished patent leather shoes, a white 
tie, a large diamnd stud and his fingers were decorated 
with daimond rings. The gentleman had the appear- 
ance of a nobleman and when he handed me his card 
which stated that he represented a glue manufacturing 
concern, I was astonished. I noticed that it seemed to 
actually be impossible for the gentleman to talk 
because of a very high starched collar he was wearing. 
It occurred to me that it would be cruel to expect my 


new acquaintance to say anything and it did seem that 
the subject of glue must be distasteful, so I politely 
informed his excellency that we are not considering 
new glues. I kept his card, however, and received sam- 
ples from time to time, but the prices were so high as 
to be prohibitive. It evidently cost this concern money 
to keep the dude on the road. 

Another instance was that of an apparently intelli- 
gent ^young man representing a prominent glue house, 
who came to my office in an intoxicated condition. He 
fairly staggered to my desk and immediately after THE "SPORT" 
introducing himself said to me in what was to be an 
undertone, that he spent the night in Toledo and had a 
h of a time. Did he get an order? 

Again, we meet the type of salesman who knows all 
about glues. He's the "candy salesman." No one has 
anything on him. He can determine glue quality by 
taking the lid off the barrel and smelling of the glue, 
or, by looking through the flake he can tell the grade. THE "EXPERT'' 
"Them there new glue testing methods ain't no good." 
Mr. Wise doesn't care what tests show, he'll tell you 
that it takes an expert like himself to select glues, leave 
it to him, he'll supply the right kind of stuff and save 
you money. 

The writer met a glue salesman a short time ago, 
who complained very bitterly about not being appreci- 
ated and the low salary his employers are paying for 
his services. I told him that I was sorry because he 
imagined his employers were trying to keep him down ; 
that I know the concern very well and that I did not 
believe them to be business men of that sort. I asked 
whether he ever thought of how much money he was 
making for his employers ? Did he make many mis- THE "CRAB" 
takes and get the concern into trouble because in some 
cases he may be overly anxious and make statements 
that cannot be fulfilled? Did he spend his leisure time 
in studying glue problems and was he familiar with 
the testing of glues, abuses, etc.? He thought a few 
minutes, then replied, "Guess you are right, have never 
thought of my position just that way." I hope the 
young man in question reads this book and especially 





this paragraph. He is invited to write to mo and to 
state whether my suggestions have proven of benefit to 
him, providing, of course, he has followed them. 

Glue manufacturers are largely to blame for select- 
ing some men to sell glues who are no more fitted for 
this vocation or profession than is the writer to drive 
an airplane. Indeed, of all the elements which go to 
make up a successful glue business, that of salesman- 
ship is most frequently neglected. Business is a profes- 
sion and a science. Salesmanship, which is a direct rep- 
resentation and most important factor in business, is 
the greatest of all professions, and is likewise a science. 
If some of you glue manufacturers, jobbers and dealers 
could watch some of the representatives I have met 
trying to sell glue, you would be tempted to boot them 
out of the office. Do not in the name of common sense 
regard salesmen as necessary evils. Train them and do 
not permit any one of them to present your cards to the 
trade nor announce their connection with your concern 
until you have every reason not to be ashamed of them. 

Instruct your salesmen to base their selling cam- 
paign on the objections that are sure to be raised. No 
salesman should ever start out without first having 
satisfactorily answered every conceivable objection 
from every point of view. 

It is singular, indeed, to observe so few advertise- 
ments from glue manufacturers. Some will tell you 
that the reason they do not advertise is because they 
employ salesmen whose business it is to call on pros- 
pectives and customers, show samples of glues and 
discuss their merits. The glue manufacturer seems to 
forget that through the advertisement published in 
good, live trade journals he will reach thousands of 
glue users at nearly the same time and the salesman 
can call on but one person at a time. It is, of course, 
true that the advertisement may not always complete a 
sale, but it will certainly pave the way for future busi- 
ness, for it will impress the name or an attractive qual- 
ity so that the reader will think of your concern when 
in the market for glues. A good ad will invariably 
influence the reader in favor of your commodity. 


The writer has heard glue makers say: "Why 
should I advertise? Supposing I list grades of glues 
based on Peter Cooper standards; I name prices 
and some competitor will answer my ad stating that 
he is prepared to offer lower prices. He will not fur- 
nish the same grades, but too few glue users test glues 
and would be unable to tell the difference, so I lose out 
because of being honest and the trickster gets the busi- 
ness." The writer must admit that this has been true, 
but we must also remember that we are all doing busi- 
ness differently than we did five or ten years ago. 
Where such a condition exists it is the best kind of ad- 
vertising to show up the cheater and by so doing the 
glue buyer will be your friend for life. 

Many glue manufacturers are doing a great deal of 
effective advertising by means of form letters, which 
are printed in imitation of typewriting. Indeed, some 
of the very best form letters I have ever perused were 
written by some genius who certainly understood the 
requirements of glue users and his letters without a FORM 
doubt "brought home the bacon." At the present time LETTERS 
printing offices in nearly all of the large cities can fur- 
nish form letters from typewriter type that are good 
imitations of typewriting. Good matching is very im- 
portant in inserting names, addresses, and other mat- 
ter in form letters. 

Glue advertisers can sometimes afford to distribute 
novelties that will keep their names before the public. 
I often wondered why manufacturers do not prepare 
printed tables for the glue buyer showing viscosity 
test, jelly, etc. It would certainly be splendid to pre- 
pare tables from different strength solutions run 
through various viscosimeters, especially the viscosi- 
meter having various sized apertures. Again, inex- 
pensive thermometers for the glue room would be 
appreciated. These novelties would likely not bring 
direct sales, but would support other advertisements 
together with the work done by your salesmen. Your 
novelty should be a constant reminder of your business 
and should be of such value so it will not be destroyed. 



THE functions of every purchasing department in 
a manufacturing establishment are: First To 
secure the most satisfactory material required in 
the manufacturing processes. Second To secure the DUTIES OF 
most desirable delivery of the material, keeping com- PURCHASING 
plete and accurate record of all unfilled purchase DEPARTMENT 

Third To obtain the best terms of payment and 
the lowest prices, quality considered. 

Fourth To record and classify materials and sup- 
plies used and purchases made. 

Fifth The buyer should have complete lists of all 
manufacturers of glues and other adhesives. He should 
keep in touch with these concerns and though he can- 
not buy from all, and, would possibly buy but from one 
or two, nevertheless, it is well to receive quotations and 
sSamples for comparison. 

The successful accomplishment of the first function 
demands that the glue buyer shall be a man who has a 
working knowledge of the particular industry for 
which he is buying this class of material. If he has in 
addition acquired the knowledge of glue testing, so 
much the better, for he will be able to make practical 
application of such knowledge. 

If care is exercised to obtain a man of the qualifica- 
tions indicated to purchase glue, there will be far less 
liability to make the error so frequently made, of buy- 
ing grades of glues good enough in themselves, but not 
exactly adapted to the particular purpose for which 
the glue is desired. 

The second function applies largely to the traffic 
department, or, in small plants proper routing should 
be specified by the glue buyer. Again, it is usually im- 
portant to ascertain at the time of purchasing the age 
of the glue and the possible date of shipment. 

To obtain the lowest price does not mean "cheap 





glue." It is to be regretted that in too many cases glue 
is considered as just glue. Some salesmen fear compe- 
tition and have no desire to enlighten the glue buyer as 
to glue standardizing. The tendency, therefore, is for 
the salesman to say that his glue is as good or stronger 
than the one the buyer is using, that it takes more 
water and as a natural consequence is a cheaper prod- 
uct so far as glue economy is concerned. The salesman 
may make price the predominating element, to substi- 
tute salesmanship for science. High grade glue costs 
money and no manufacturer can afford to sell an 
article for fifty cents that possibly costs him one dollar 
to produce in his factory. Nevertheless, prices may be 
unreasonably higher and the buyer should possess the 
ability to determine the lowest just and fair price, the 
quality of the material considered. 

It is well to list manufacturers, jobbers and dealers 
selling glue on suitable tray cards. The card should 
give the name of the manufacturer, jobber or dealer, 
address, grades of glues manufactured, financial rating 
(the financial rating being a fairly good barometer to 
show whether or not the manufacturer, jobber or 
dealer is financially able to carry out the terms of the 
crder of contract.) The card should also show the kind 
of glue manufactured, hide, bone, vegetable, water- 
proof or any other adhesive. The buyer should ascer- 
tain, if possible, what grades of glues the manufac- 
turer, jobber or dealer specializes in. The manufac- 
turer of paper boxes would likely not be interested in 
high grade hide glues and the wood worker would not 
find the box-maker's glue practical in his line of work, 
therefore, it would not be advisable to list all grades of 
glues and the manufacturers, jobbers or dealers handl- 
ing the grades and kind of glues you do not require. 

The back of this card may be arranged in columns 
for the purpose of entering quotations. The first col- 
umn would show the date, the second manufacturer's 
or jobber's number of the glue boiling; the third, grade 
of glue; fourth, the number of unsold pounds in the 
boiling; fifth, F. 0. B. point; sixth, price; seventh, 
terms. Ordered columns may also be provided on the 


back side of the card. First column showing the date 
and second, quantity ordered. 

The glue buyer must insist upon receiving timely 
requisitions from all the departments requiring glue. 
Under ordinary circumstances the purchaser of glues RE Q U J SITIONS 
should place no orders until he has first received a REQUn 
requisition from either the stores department or the 
department that requires material. 

A positive rule should be laid down that all glue 
requirements be anticipated in ample time so that the 
buyer will not be compelled to purchase unsatisfactory 
stock from possibly a nearby dealer so as to avoid a 
"shut-down." Again, requisitions should be signed or 
countersigned by either the foreman requiring the ma- 
terial or the superintendent. Requisitions can, of 
course, be drafted to meet individual requirements. 

When contracts are made involving a large invest- 
ment, considerable testing and investigating will be 
necessary and the writer's experience has been that it 
will require from thirty to sixty days to get samples, 
test them, receive quotations and finally decide upon 
the glue that will be contracted for. . 

Departments requiring glue or store rooms should 
carry what may be termed a "Low Stock Report." The 
glue should be given a low limit and when this is 
reached the workmen, foreman, stores-keeper or who- 
ever has charge of the glue should report promptly to 
the person issuing the requisitions. 

It is also imperative to keep a complete record of all 
tests and to file them for future reference. A vertical 
two-drawer bill file cabinet answers this purpose very 
nicely. In the top drawer file favorable reports. In the 
second drawer the unfavorable. The advantage of this KEEP A 
scheme is apparent, for it is a simple matter to deter- RECORD or 
mine within a few moments who supplied the best and TESTS 
who the poorest samples. All test cards, good or poor, 
should be filed. I have found this scheme especially 
valuable in calling the bluffs of glue salesmen who per- 
sist in knocking their competitors' glues. 

The manufacturer spending money in the way of 
the salesman's salary, railroad and hotel expenses de- 




serves consideration. It is to be regretted that many 
glue buyers do not appreciate this and in many cases 
glue salesmen representing the most successful and 
reliable glue houses are turned down not even given 
an audience. When a salesman spends time and money 
to visit you, he has something to say and if you are a 
good buyer you will permit him to have his say. To be 
sure there are many men who suppose the buyer has 
no other duties than to listen to stories, smoke cigars, 
and be a good fellow. The writer usually allowed every 
salesman from five to ten minutes and he was given to 
understand when entered my office that he must be 

Another suggestion: Whenever you find a boiling 
that is highly satisfactory, buy the entire boiling. Of 
course, the writer appreciates that small manufactur- 
ing plants cannot at all times avail themselves of such 
offerings, however, the glue manufacturer may reserve 
a certain quantity or possibly all of the boiling for the 
small manufacturer, especially so if a reasonable de- 
posit is made or a liberal amount taken in on the first 
shipment. When buying the entire boiling you know 
absolutely just what you are receiving. The writer 
has never regretted doing this. 

If the buyer of glues will avail himself of the infor- 
mation given he will avoid excessive buying, inferior 
quality, high prices and poor deliveries. Right buying 
means an improvement in the quality of the goods, 
increased production, and, last but by no means least, 
satisfied customers. 



THE average paper box manufacturer buys very 
cheap glue. This is usually a bone product of the 
lowest grade. It is possible to use almost any 
kind of glue in the manufacture of paper boxes and the 
real factor is the price. It is, of course, imperative to 
select glues that are not in the stages of decomposition 
and the tests explained in this book, when properly 
applied, are all the information that is required to 
determine this point. Again, in boxes that are printed m 

i i .. -i -i i-ii br*L,LCTlO,N OF 

or colored it is necessary to avoid glues that are too GLUE FQR 
strongly alkali or acid. The litmus tests explained for PAP 
acidity or alkalinity must be applied. If the paper box 
maker will study all the information explained in the 
pages of this treatise he will eliminate all of his glue 
troubles. It will be appreciated that it takes but little 
glue room abuse to almost destroy the adhesiveness of 
a cheap or low grade glue. Watch the temperature. 
When heated, all glues are gradually killed and the 
damaging action begins as soon as the temperature of 
the solution reaches 120 degrees. Unfortunately a 
slightly higher temperature than the temperature at 
which damage to glue begins is quite necessary, never- 
theless, common sense must enter into the problem 
and if the paper box makers will exercise great care 
they can obtain a higher degree of efficiency and in 
many cases greatly improve the quality of their 

The novice will be surprised to observe the possi- 
bilities of box making machines. There are a number 
of popular machines ; we will, however, discuss the B0 x MAKING 
merits of but three. MACHINES 

The Jagenbry Box Making Machine automatically 
feeds the cut out blanks, forms the box, glues, applies, 
cuts strip paper and turns striper in and over. 

The Staude Automatic Folding Box Gluer will auto- 
matically feed blanks one at a time at a high speed, 





glue, fold, count and stack in a vertical pile that keeps 
the glued seam under pressure so it cannot pop open. 

There is a possibility of combining vegetable and 
mineral adhesives such as starch solutions and flour 
pastes and silicate of soda. The essential requirements 
would here be that the vegetable part should not con- 
tain any considerable excess of free alkali. 

Most box makers have their own private formulas. 
One of the points to remember when working out a 
formula for a paper box adhesive is the setting of the 
glue. Of course, we know that the lower the tempera- 
ture in the work-room the lower the temperature of 
the warm liquid glue, and the higher the grade of the 
glue, the quicker will the glue set. 

For the building of chip or container board silicate 
of soda is used. The stock is built up the same as ply- 
wood. The only pressure applied, however, is on the 
machine when the stock goes through the squeeze rolls. 
Silicate of soda has much less water in it than is used 
with other adhesives and the various grades are pro- 
duced with considerable latitude in setting. 

It requires from fifteen to twenty pounds of silicate 
to build up 1,000 square feet of three-ply board, 15 
pounds as minimum and 20 pounds as maximum. It 
varies between these two points on different grades of 
paper. Each additional ply will require from 71/2 to 10 
pounds additional silicate of soda. A three-ply board 
has two pasted sides. A four-ply board has three 
pasted sides, each side requiring 7 l /9 to 10 pounds of 
silicate of soda per 1,000 square feet irrespective of 
caliper of the board. 

Silicate of soda is packed in either wooden barrels 
or metal drums, both containing approximately 600 
Ibs. The barrels have two openings, one in the center 
and one in the head, and the silicate can be drawn from 
the same with a good sized spigot, say one inch inside 
opening. The user should always draw from the barrel 
in a small container the desired amount for one day's 
use, and when the brush is not in use the bristles 
should be submerged in water, which will preserve 



EVERY office and department in any manufactur- 
ing plant requires system and organization. 
When these important factors are neglected the 
quality of the goods is certainly compelled to suffer and 
the manufacturer usually realizes a loss instead of a 
gain. No manufacturer is in business for his health. 
He cannot "break even" year after year and he is 
either making or losing money. The woodworking 
manufacturer knows that it costs money to repair open 
joints or blistered and loose veneers. It isn't always 
the fault of the glue, as has been generally charged, 
and I know from experience that in most cases the 
workmen or the system are at fault. Our first duty is 
to select the grade or grades of glue that will give 
reliable results. When selecting glue for wood work 
we must insist upon receiving the purest glue avail- 
able, glue that is not loaded with chemicals to give 
fictitious value. The writer has already explained the 
requirements of various lines and we will not here 
repeat anything that has been stated. 

It is immaterial whether we manufacture matches, 
emery wheels, cloth, paper boxes, furniture, caskets, 
pianos, etc. We are all interested in glue that holds. It 
is an absolute fact though that different workmen may 
get different results with the same glue all made in one 
boiling at the glue factory. Why such differences ? The 
answer is simply, that every one of the men may abuse 
the glue, one more than the other and when used the 
quality is not the same high grade as when originally 
dropped in the glue cooker. 

The one feature that is an absolute essential to the 
proper working or handling of glue is intelligence. We 
want to forget that any Tom, Dick or Harry can pre- 
pare glues, and all you need give him is a few pails, a 
quantity of glue and show him where the faucet is so 
that he can prepare the glue for "soaking." We must 






train our men, and to do so every manufacturer, large 
or small, can well afford to place our glue books in the 
various departments so that the workmen can learn 
how glue should be prepared and properly handled to 
get 100% efficiency. The workmen who master all this 
book contains may rightly call themselves experts, and 
if this is done the manufacturer will then have the 
assurance that glue room troubles are a thing of the 
past. I did not incorporated this statement to boost the 
sale of the book, but this is absolute truth and the 
writer has in mind only the welfare of his readers. 

Practically every department in a manufacturing 
plant has one or more foremen. These men are singled 
cut to oversee the work. This should also be done in 
the glue room. Single out the most intelligent man you 
have in that department and hold him responsible. 
This need not be the foremen for the reason that these 
men have too many details and they likely cannot give 
the preparation, distribution and using of the glues the 
close and careful attention so necessary if quality is to 
be realized. 

Proper equipment is very necessary. We are going 
to discuss equipment in another chapter so will next 
direct your attention to the temperature of the glue 
room. We all know how imperative it is to have a 
fairly uniform temperature in varnish rooms. Your 
glue room is just as important. Again, you avoid draft 
in the varnish room and we must do so in the glue 
room. Chilled glue will cause trouble and when the 
stock is too hot, owing to a very high temperature in 
the gluing department, the men are uncomfortable. 
Some men insist upon heating the wood until so hot 
that one cannot touch the heated surface with the 
naked hand. When wood is heated hot, too much glue 
is taken up. Then when the wood cools off the air in 
the pores beneath the glue contracts as it cools, creat- 
ing a suction which draws the glue farther into the 
wood, and this is liable to seriously affect the joint for 
there may be a little glue left on the surface, as it is all 
absorbed by the wood. 

Having the ideal glue room conditions and the most 


suited stock for our peculiar requirements, we must 
measure the glue and water. Hundreds of manufac- 
turers in all lines of business neglect doing this and the 
men pour water on the dry glue until the surface has GLUE AND 
been covered. Weigh your water as well as the glue W ATERMUST 
and watch the proportions very carefully. BE WEIGHED 

The function of soaking is to get back into the 
glue the liquid it originally contained. Precautions 
must be observed that will insure uniform softening 
prior to melting. Very frequently one finds long or 
wide flakes. It is well to break them into suitable sizes 
prior to soaking. Do not permit pieces to stick out of 
the water. All of the glue must soak and unless this 
is the case it will take a considerably longer time to 
melt than if soaked properly before applying heat. 
Many so-called "glue experts" object to soaking the 
glue over night. This is perfectly right in the case of 
flake glues, providing, of course, the room is not too 
hot. Hot summer nights are not very desirable. Glues 
should not be soaked too long as too much soaking kills 
the strength. Thin cut, high-test glues absorb water 
rapidly. They will therefore soak in a much shorter 
time than thick glues. This applies as well to ground 
glues. A very good plan is to pour water (taken from 
the quantity weighed) into the soaking container so 
that when adding the glue it will surely become soaked. 
Unless this is done you are taking chances and there 
may be particles or flakes at the bottom that will not 
become saturated. Stir again and again. This will 
assist very much and will to some extent shorten the 
time of the soaking. 

Use only pure, cold water. Some men seem to be 
under the impression that there is no better water 
than that which has been chemically treated in the 
boiler for the prevention of scale. The writer at one 
time visited a woodworking plant having consider- DO NOT USE 
able trouble with glue. The grade was splendid, the BOILER 
men did not appear to overheat it and the entire prob- WATER 
lem had me guessing until I saw a workman coming up 
the stairs with two pails of water. I immediately be- 
came suspicious, and asked him for what purpose he 





intended the water. He replied, to soak the glue. I 
said, "Haven't you water faucets in your glue room?" 
He replied, "The clearest water we can possibly get is 
water that has been softened and this comes from the 
boiler." Here was the answer. 

Again, I observed men drawing water from the 
water jacket in the glue cooker. This sort of thing is 
inexcusable and should not be tolerated in any glue 

We have perused hundreds of articles in trade 
papers dealing with the subject of overheating glues. 
Every salesman cautions us against this evil. We feel, 
therefore, that little information is necessary along 
this line. However, for the benefit of any reader who 
may not know what damaging effects heat has on glue, 
I want to state that the most desirable temperature to 
heat glue is approximately 148 degrees F. For some 
classes of work from 138 up to 145 is perfectly safe. 

The moment a mixture of glue and water is heated 
enough to melt it a gradual change begins to take place 
in such a way that the water-taking or spreading capa- 
city of the glue is gradually destroyed. It is caused by 
the water attacking the glue and heat increasing the 
effect of the attack. 

Heat should be applied indirectly. That is, do not 
permit steam to come in direct contact with the glue. 
Open iron kettles should never be employed. Of course, 
there is always more or less evaporation in glues. How- 
ever, if the cookers or glue pots are closed this evapo- 
ration would, to a great extent, be eliminated. The con- 
struction of the glue cookers, pots, tanks, etc., is there- 
fore of great importance. Our grandfathers would 
work with open iron kettles. Shavings, sawdust and 
foreign matter would be conspicuous in the glue pots. 
Therefore, they found it necessary to add more dowels 
or drive more nails to assist the glue in holding than is 
necessary today. We could, of course, go into details 
regarding cookers. However, there are a number of 
very good dissolvers or commonly called "glue cook- 
ers," on the market and every manufacturer makes 
certain claims for his product. The writer suggests 


though that the buyer be very careful and that he buy 
only such glue room equipment as will give lasting 

The equipment being right, there should be no 
trouble upon obtaining a uniform melt at the minimum 

You would not think of operating your boilers 
without water and steam gauges. Therefore, it is im- 
perative that you provide thermometers to your cook- 
ers, glue pots and glue spreaders. The automatic tem- 
perature controller is a wonderful appliance and by its 
use the supply of heat is automatically regulated. 

When melting do so slowly. Every experienced glue 
user knows that there is nothing to be gained by at- 
tempting to dissolve the glue within a few minutes and MELT QLUE 
that when this is attempted a scum is formed over the SLOWLY 
glue, preventing its proper melting. 

It is well to prepare two or three batches a day or 
more if necessary. Do not prepare so great a quantity 
that enough glue is dissolved to last three or four days. 
A glue solution when allowed to cool and then is re- 
melted has not the same tenacity as a freshly prepared 
solution. Consequently, for ordinary work, the quan- 
tity of glue solution prepared should not be more than 
is required for immediate use. 

The melting pots should be kept perfectly clean. 
Much unnecessary waste may be avoided through ob- 
servance of cleanliness. After the melted glue becomes 
sour, and, unless this sour glue has been removed from 
the melting pot it will spoil the fresh solution. Do not, 
therefore, tolerate dirty pots and do not, under any 
circumstances, mix or permit a mixture of old dis- 
solved and new glue. 

Again, do not permit glue to freeze. If glue jelly is 
frozen through it will crumble and act about like over- ^ NOT ALLOW 
heated glue. 

Do not use the glue until it has thoroughly melted. 
So many glue users seem to labor under the impression 
that partly dissolved glue can be used with perfect 
safety. This is wrong and should not be put into 


Do not permit the temperature of the glue to raise 
or lower. Keep it uniform. 

Store glue in a dry place and do not unhead the 
barrels until you are ready to use the glue. 

Co-operation is absolutely necessary in every line 
of business, and in every department. Your men will 
be glad to co-operate if given a chance. Having per- 
fected your organization so that you know absolutely 
that you are receiving 100% glue room efficiency, do 
not forget the men who are assisting you in making 
this possible, and, the men who are actually doing the 
CO-OPERATE work. When yoyr men are doing good work, be big 
WITH YOUR enough to go to them and tell them so. This requires a 
MEN little giving on the part of the employer, superinten- 

dent or foreman, but it is no expense it is merely the 
giving of credit where it is due. As your men improve 
in your service their incomes should improve. The pay 
envelope and the occasional word of commendation are 
powerful tools that you have at your command for a 
persistent sequence of growth toward a better 













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